EPA_625/4-77-003a
/" Status of
Oxygen-Activated Sludge
Wastewater Treatment
EPATechnology Transfer Seminar Publication
-------
EPA 625 4-77-003a
STATUS OF OXYGEN-ACTIVATED
SLUDGE WASTEWATER TREATMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ENVIRONMETNAL RESEARCH INFORMATION CENTER • Technology Transfer
October 1977
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ACKNOWLEDGEMENTS
This publication contains materials prepared for the U.S. Environ-
mental Protection Technology Transfer Program and presented at
municipal pollution control seminars across the United States. It re-
places the previous Technology Transfer seminar publication on this
subject originally published in 1973.
Richard C. Brenner, U.S. EPA, Municipal Environmental Research
Laboratory, Cincinnati, Ohio prepared this publication.
NOTICE
The mention of trade names or commercial products in this publication is
for illustration purposes, and does not constitute endorsement or recommenda-
tion for use by the U.S. Environmental Protection Agency.
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CONTENTS
Introduction 1
Chapter 1 - Status Report 2
Chapter 2 — Description of Second Generation Open Reactor Oxygen System (Marox). . 12
Chapter 3 - Case Histories , 21
Decatur, Illinois 22
Detroit (#1), Michigan 25,
Fairfax County, Virginia 28
Gulf States Paper Corporation, Tuscaloosa, Alabama 32
Lederle Laboratories, Pearl River, New York 34
Littleton, Colorado 36
Morganton, North Carolina 37
North Lauderdale, Florida 39
Speedway, Indiana 41
Union Carbide Corporation, Sistersville, West Virginia 43
Winnipeg, Manitoba 44
Information Sources 46
References 47
in
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INTRODUCTION
In the past eight years, the use of oxygen gas in the activated sludge process has evolved from a
level of primarily academic interest to a point of broad application and implementation. A large and
rapidly growing number of oxygen-activated sludge plants are in operation in North America and
Japan. Several plants will soon be operational in Europe. Included among the operating facilities are
installations treating process wastewaters from six major industrial categories. By 1980, it is project-
ed that construction will be completed on approximately 150 oxygen systems with a combined
hydraulic capacity between 5 and 6 bgd (219 to 263 cu m/sec).
Beginning with the initial research project conducted at Batavia, New York, in 1968 and 1969
(1), the development and refinement of oxygenation technology has been more rapid than normally
associated with wastewater treatment processes. Design engineers today can select from several
oxygen dissolution concepts including both covered and open reactor alternatives. The covered
reactor UNOX and OASES systems (marketed by the Union Carbide Corporation and Air Products
and Chemical) are available with either surface aerators or submerged turbines. The surface aerator
option has become the standard covered reactor design except in cases where unusually deep tanks
are specified. Two versions of open reactor MAROX system (marketed by the FMC Corporation),
one utilizing rotating active diffusers (RAD's), the other fixed active diffusers (FAD's), are also
marketed. At this time, the second generation RAD design appears to be a significant cost-effective
improvement compared to the original FAD design.
The purposes of this publication are:
1. To provide an updated status report on the number and type of oxygen-activated sludge
facilities in operation, under construction, and being designed.
2. To describe in detail the latest EPA supported oxygenation research and demonstration
project, an evaluation of the RAD version of the open reactor system being carried out at the
Metropolitan Denver, Colorado Sewage Treatment Plant.
3. To summarize design, operating, and performance information for several on-line oxygen
wastewater treatment systems.
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Chapter 1
STATUS REPORT
A complete listing of the 50 oxygen-activated plants that were in operation as of June 1976
is presented in Table 1-1. The 66 oxygenated plants under construction on the same date are
listed in Table 1-2. An additional 41 oxygenation plants were in various stages of design during
June 1976; these plants are listed in Table 1-3.
All three tables provide design flow and oxygen supply data (where known) for each plant
location listed, as well as identifying the wastewater application. Multiple oxygen process applica-
tions, such as carbonaceous organics removal plus nitrification, aerobic digestion, ozonation, etc.,
are also noted where applicable. In addition, Tables 1-1 and 1-2 include information on the oxygen
supply systems selected. This latter information is not given in Table 1-3 because these plants have
either not yet been bid or litigation has delayed awarding of contracts to specific oxygen system
suppliers.
Perusal of Table 1-3 reveals that no industrial wastewater applications are shown in the
"plants being designed" list. This omission is not intended to indicate that there were no indus-
trial plants in the design phase as of June 1976, but rather that the identity of such plants is
confidential proprietary information until after equipment purchase contracts are awarded.
Data on the number of plants, design flows and oxygen supply capacities have been extracted
from Tables 1-1, 1-2 and 1-3 and condensed in Table 1-4. The same information is presented in
Table 1-5 for United States oxygen plants. These two tables indicate that as of June 1976 only
about 12 percent of the firm planned oxygen design flow capacity was actually completed and in
operation. On-line capacity is expected to increase 7-8 times, however, in the next 4-5 years. Ap-
proximately 25 percent of the oxygen installations included in the Table 1-4 totals were treating or
will treat industrial process wastewaters. Excluding the Japanese plants for which oxygen supply
data were unavailable to the writer, the design oxygen supply capacity averages 3.07 tons/mil gal
of design flow (7.4 x 10~4 metric ton/cu m) for the industrial applications compared to 1.34 tons/
mil gal of design flow (3.2 x 10~4 metric ton/cu m) for the municipal applications.
A breakdown, by country, of the 157 known operating and planned oxygen installations is
given in Table 1-6. Eighty-five percent of these installations are or will be located in the United
States and 11 percent in Japan. The remaining 4 percent are divided among seven other countries
each with one plant.
The detailed information provided in Tables 1-1 and 1-2 on oxygen dissolution and oxygen
generation systems is summarized in Table 1-7. In most cases, the vendor supplying the oxygen
dissolution equipment was also awarded the oxygen supply system contract. The preponderance
of surface aerators over submerged turbines in covered reactor systems is illustrated in Table 1-7
and is attributed to the lower overall costs and maintenance requirements of the aerator option.
Surface aerators are being or will be used in 93 percent of the covered reactor systems with speci-
fied dissolution equipment, submerged turbines in 6 percent, and a combination of both in one
system. Plants employing submerged turbines have deep aeration tanks, typically greater than 20
ft (6.1 m), and tend to be larger than 100 mgd (4.4 cu m/sec) in size. Conversely, the average de-
sign flow of the 103 surface aerator systems is only about 18 mgd (0.8 cu m/sec).
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Table 1-1. Oxygen-Activated Sludge Plants In Operation as of June 1976
Location
USA
1. Alton Box Board - Jacksonville, Fla.
2. Baychem Corp., Chemagro Div. -
Kansas City, Kan.
3. Brunswick, Ga.
4. Chaska, Minn.
5. Chesapeake Corp. - West Point, Va.
6. Container Corp. -
Fernandino Beach, Fla.
7. Decatur, III.
8. Deer Park, Tex.
9. Denver (#2), Colo.
10. Detroit (#1), Mich.
11. Fairfax County, Va.
12. Fayetteville, N.C.
13. Fibreboard Corp. - Antioch, Calif.
14. Ft. Myers, Fla.
15. French Paper Co. - Niles, Mich.
16. Gulf States Paper Corp. -
Tusaloosa, Ala.
17. Hamburg (#1), N.Y.
18. Hercules, Inc. - Wilmington, N.C.
19. Hollywood, Fla.
20. Jacksonville (#1), Fla.
21. Lederle Laboratories Div. of
American Cyanamid-Pearl River, N.Y.
22. Littleton, Colo.
23. Morganton, N.C.
24. Morrisville, Pa.
25. Newtown Creek - New York City, N.Y.
26. North Lauderdale, Fla.
27. Quail Valley, Tex.
28. Speedway, Ind.
29. Standard Brands - Peeksville, N.Y.
30. Union Carbide Corp. - Marietta, Ga.
31. Union Carbide Corp.-
Sistersville, W. Va.
32. Union Carbide Corp. - Taft, La.
33. Weyerhauser Corp. - Everett, Wash.
34. Wyandotte, Mich.
35. Yuba City, Calif.
TOTAL
Design
Flow
(mgd)
6
4.32
10
1.25
16.25
25
17
5
10
300
14
14
16
5
0.8
10
1
1
36
5
1.5
1.5
8
4.6
20
2
1.5
7.5
1
1.26
4.33
3.8
3
100
7
664.61
Installed
O2 Supply
Capacity
(tons/day)
25
50
16
1.25
34
50
17
6
7.5
180
10
18
35
9
1
30
0.5
15
50
20
15
0.5
26
4
14
1
2
4
5
1
15
88
25
60
21
856.75
Appli-
cation^:
I-PP
I-C
M
M
I-PP
I-PP (b)
M
M
M
M
M
M
l-PP(b)
M
I-PP
I-PP
M
I-C
M
M
I-PH
M(d)
M
M
M
M(d)
M
M
-FP
-C
-C
-PC
-PP
M
M
O2 Dis-
solution
Systems§
UNOX (A)
UNOX (A)
UNOX (A)
OASES (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
MAROX (R)
UNOX (T)
OASES (A)
OASES (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
OASES (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (T)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (T)
UNOX (A)
UNOX (T)
UNOX (A)
02
Supply
Systems
CRYO
CRYO
PSA
LIQ
CRYO
CRYO
PSA
PSA
LIQ
CRYO
LIQ
CRYO
PIPE
PSA
LIQ
PSA
LIQ
PIPE
CRYO
PSA
PSA
LIQ
PSA
PSA
PSA
LIQ
PSA
PSA
LIQ
LIQ
PIPE
PIPE
PIPE
PSA
PSA
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Table 1-1. (Continued)
Location
Canada
1. Winnipeg, Manitoba
Japan
1. Electro Chemical Industrial Co. -
Ichihara City
2. Gotsu Plant - Katano City
3. Ikuta Plant - Kawasaki City
4. Jujo Paper - Kushiro City
5. Kasuga Plant - Oita City
6. Mitsubishi Chemical Industries -
7. Nissho Kayaku Petrochemical
Complex - Oita City
8. Oji Paper - Kasugai City
9. Oji Paper - Tomakomai City
10. Sanyo Kakusaku Pulp - Iwakuni City
11. Showa Neoprene - Kawasaki City
12. Sumitomo Chemical - Ichiha'ra City
13. Uenodai Plant, Japan Housing Corp. -
Kamifukuoka City
14. Yakult Pharmaceutical Industries -
Osaka City
TOTAL
|I-C = Industrial-Chemicals
I-FP - Industrial-Food Processing
I-PC - Industrial-Petrochemical
I-PH = Industrial-Pharmaceutical
I-PP = Industrial-Pulp & Paper
I-SR = Industrial- Synthetic Rubber
M = Municipal
(b) = Conventional 02 treatment plus
Design
Flow
(mgd)
12
2.64
0.73
0.61
1.59
0.26
1.9
0.74
18.5
13.2
0.89
0.79
0.79
0.52
0.19
43.35
*
Installed
O2 Supply
Capacity
(tons/day)
10
n.d.**
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
PSA = On-site
oxygen
*n.d. = no data
Appli-
cation!
M
I-PC
M
M
I-PP
M
I-PC
I-PC
I-PP
I-PP
I-PP
I-SR
I-PC
M
I-PH
pressure
O2 Dis-
solution
Systems§
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
MAROX (R)
O2
Supply
Systems*
PSA
n.d.**
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
swing adsorption
gas generation
(d) =
black liquor oxidation
Conventional C>2 treatment plus
aerobic sludge digestion
§MAROX = FMC Corp.
OASES = Air Products & Chemicals, Inc.
UNOX = Union Carbide Corp.
(A) = Surface aerators (with or without
bottom mixers)
Fixed active diffusers
Rotating active diffusers
Submerged turbines
= On-site liquid oxygen gas generation
LIQ = On-site liquid oxygen storage and
vaporization
PIPE = Pipeline transport of oxygen gas from
a nearby off-site oxygen generating facility
(F)
(R)
(T)
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Table 1-2. Oxygen-Activated Sludge Plants Under Construction as of June 1976
Location
Design
Flow
(mgd)
Installed
O2 Supply
Capacity
(tons/day)
Appli-
cation^:
O2 Dis-
solution
Systems§
02
Supply
Systems«
USA
1. Appleton Papers Div. of N.C.F. -
Appleton, Wise.
2. Baltimore, Md.
3. Baton Rouge, La.
4. Broken Arrow, Okla.
5. Cedar Rapids, Iowa
6. Chicopee, Mass.
7. Cincinnati, Ohio
8. Crown Zellerbach Corp. -
Antioch, Calif.
9. Dade County (North), Fla.
10. Danville, Va.
11. Denver (#1), Colo.
12. Detroit (#2), Mich.
13. Dow Chemical Co. - Plaquemine, La.
14. Dubuque, Iowa
15. Duluth, Minn.
16. East Bay Municipal Utility District
(#1) - Oakland, Calif.
17. East Bay Municipal Utility District
(#2) - Oakland, Calif.
18. Euclid, Ohio
19. Exon Chemical Co.-Baton Rouge, La.
20. Fairbanks, Alaska
21. Fond du Lac, Wise.
22. Ft. Lauderdale, Fla.
23. Harrisburg, Pa.
24. Hillsboro, Ore.
25. Hopewell, Va.
26. Hot Springs, Ark.
27. Jacksonville (#2), Fla.
28. Kittanning, Pa.
29. Lewisville, Tex.
30. Littleton/Englewood, Colo.
31. Longview Fiber - Longview, Wash.
32. Louisville, Ky.
33. Loxahatchee, Fla.
34. Mahoning County, Ohio
35. Miami, Fla.
36. Middlesex, N.J.
37. Minneapolis, Minn.
38. Mobile, Ala.
39. Mosinee Paper Corp.-Mosinee, Wise.
40. Muscatine, Iowa
41. Nekoosa Papers, Inc.
Port Edwards, Wise.
42. New Orleans, La.
43. North San Mateo, Calif.
44. Pensacola, Fla.
45. Philadelphia (Southwest), Pa.
46. Pima County, Ariz.
6.5
70
16
4
33
15.5
1.2
5.5
60
24
72
600
12.7
16
43.6
14
75
12
3.5
120
17
50
10
100
33
80
450
69
26
80
I-PP
M
M
M(d)
M
M
M(Z)
I-PP
M
M
M
M
I-C
M
M
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
OASES (A)
UNOX (A)
UNOX (A)
OASES(T&A)
UNOX (A)
OASES (A)
UNOX (A)
PSA
CRYO
PSA
LIQ
CRYO
PSA
CRYO
PSA
CRYO
PSA
CRYO
CRYO
PIPE
CRYO
CRYO
120
250
M
UNOX (T) CRYO
1.5
22
9
8
11
22
35.4
15
57.63
12.1
5
1.5
6
20
30
105
4
4
55
120
1
28
6
13
35
122
8
24
210
25
1.5
28
35
13
26
55
50
9
100
11.5
16
1
7
21
40
100
9
7
80
450
1
26
13
80
52.8
140
10
40
90
22
M
M
I-PC
M(d)
M
M(n)
M
M
M
M
M
M
M
M
I-PP
M
M(n)
M(n)
M
M(d)
M
M
I-PP
M
l-PP(b)
M
M
M(n&o)
M
M
MAROX (R)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
OASES (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
MAROX (R)
UNOX (A)
UNOX (T)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (T)
MAROX (F)
UNOX (A)
UNOX (A)
UNOX (A)
UNOX (A)
OASES (A)
UNOX (A)
OASES (A)
UNOX (A)
UNOX (A)
PIPE
PSA
CRYO
PSA
PSA
CRYO
CRYO
PSA
CRYO
PSA
PSA
PIPE
PSA
CRYO
CRYO
CRYO
PSA
PSA
CRYO
CRYO
LIQ
PSA
PSA
CRYO
CRYO
CRYO
PSA
CRYO
CRYO
PSA
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Table 1-2. (Continued)
Location
47. St. Regis Paper Co. - Tacoma, Wash.
48. Salem, Ore.
49. Shell Oil Co. - Norco, La.
50. Springfield, Mo.
51. Sunkist Growers, Lemon Products
Div. - Corona, Calif.
52. Tahoe/Truckee, Calif.
53. Tampa, Fla.
54. Tauton, Mass.
55. Thilmany Pulp & Paper Co. -
Kaukauna, Wise.
56. Tonawanda, N.Y.
57. Two Bridges, N.J.
TOTAL
Mexico
1. Fundidora Steel Co. - Monterrey
Europe
1. ARA SIRS II, Switzerland
2. Bayer-Elberfeld -
Dusseldorf, Germany
3. Copenhagen, Denmark
4. Palmersford, England
5. Union Carbide Belgium -
Antwerp, Belgium
TOTAL
Japan
1. Mitsubishi Chemical Industries -
Kitakyushu City
2. Mitsui Toatsu Chemicals -
Takaishi City
3. Tokiwa Sangyo - Owan Asahi City
TOTAL
t-l-C = Industrial-Chemicals
I-DS = Industrial-Dyestuffs
I-FP - Industrial-Food Processing
I-PC = Industrial-Petrochemical
I-PP - Industrial-Pulp & Paper
I-S = Industrial-Steel
Design
Flow
(mgd)
34
26.5
4.3
30
1.75
8
51
8.4
22
30
7.5
2339.58
13.7
18
1.8
110
1.2
0.71
131.71
3.09
1.71
3.7
8.50
Installed
O2 Supply
Capacity
(tons/day)
40
36
50
36
50
4
120
20
10
32
6
3328.3
12.7
20
50
160
2
16
248
n.d.**
n.d.
n.d.
UNOX
(A) =
(F) =
(R) =
(T) =
M = Municipal "CRYO
(b) = Conventional O2 treatment plus black
liquor oxidation . .Q
(d) - Conventional O2 treatment plus aerobic
sludge digestion PIPE
(n) = Conventional O2 treatment plus nitrification
(o) = Conventional O2 treatment plus
effluent ozonation po/\
(Z) = Treatment of Zimpro supernatant only
§MAROX = FMC Corp.
O2 Dis- O2
Appli- solution Supply
cation:): Systems§ Systems*
I-PP UNOX (A) CRYO
M UNOX (A) PSA
I-PC UNOX (A) CRYO
M(O3) UNOX (A) PSA
I-FP UNOX (A) CRYO
M UNOX (A) PSA
M(n) UNOX (A) CRYO
M(n) UNOX (A) CRYO
I-PP UNOX (A) PSA
M UNOX (A) CRYO
M UNOX (A) PSA
I-S UNOX (A) PIPE
M UNOX (A) PSA
I-C UNOX (A) CRYO
M UNOX (A) CRYO
M(n) UNOX (A) PSA
I-C UNOX (A) PSA
I-DS UNOX (A) n.d.**
I-PC UNOX (A) n.d.
I-PP UNOX (A) n.d.
= Union Carbide Corp.
Surface aerators (with or
without bottom mixers)
Fixed active diffusers
Rotating active diffusers
Submerged turbines
= On-site cryogenic oxygen
gas generation
= On-site liquid oxygen storage
and vaporization
= Pipeline transport of oxygen
gas from a nearyby off-site
oxygen generating facility
= On-site pressure swing adsorption
oxygen gas generation
OASES = Air Products & Chemicals. Inc. "n-d- = no aata
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Table 1-3. Oxygen-Activated Sludge Plants Being Designed as of June 1976
Location
USA
1. Amherst, N.Y.
2. Augusta, Me.
3. Baldwinsville, N.Y.
4. Clay, N.Y.
5. Clinton, N.C.
6. Concord, N.C.
7. Dade County (South), Fla.
8. Easton, Pa.
9. Greenville, S. C.
10. Hamburg (South Towns), N.Y.
11. Hampton Roads Sanitary District, Va.
(a) Army Base
(b) Atlantic
(c) Boat Harbor
(d) Lamberts Point
12. Hannibal, Mo.
13. Holyoke, Mass.
14. Houston, Tex.
15. Indianapolis (Belmont), Ind.
16. Indianapolis (Southport), Ind.
17. Kansas City, Kan.
18. Kaukauna, Wise.
19. Lebanon, Pa.
20. Los Angeles (Hyperion), Calif.
21. Los Angeles County (JWPCP), Calif.
22. Maryland City, Md.
23. Montgomery County, Pa.
24. Monticello, N.Y.
25. Murfreesboro, Tenn.
26. New Rochelle, N.Y.
27. Orlando, Fla.
28. Passaic Valley, N.J.
29. Philadelphia (Northeast), Pa.
30. Philadelphia (Southeast), Pa.
31. Red Springs, N.C.
32. Sacramento, Calif.
33. San Francisco, Calif.
34. South Cobb County, Ga.
35. Sussex County, Del.
36. Tri-Municipal Sanitary District
Poughkeepsie, N.Y.
37. York, Pa.
38. Texas City, Tex.
TOTAL
Design
Flow
(mgd)
24
8
9
10
3
25
40
10
5
12
19
36
26
37
4.25
22
200
125
125
54
6.1
8
330
500
4
10
6
8
14
24
300
150
100
1.5
150
180
24
8
14
8
75
2647.35
Design
O2 Supply
Capacity
(tons/day)
40
9
19
10
9
80
130
14
8
14
21
40
30
42
9
22
305
180
180
80
13
24
340
500
7
14
6
13
16
50
1000
100
80
5
200
100
40
11
9
13
11
3794
Appli-
cation^
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
M
:j:M = Municipal
-------
Table 1-4. Worldwide Oxygen Plant Status — June 1976
Parameter
No. of Plants
Municipal
Industrial
Total
Design Flow (mgd)
Municipal
Industrial
Total
O2 Supply Capacity-f (tons/day)
Municipal
Industrial
Total
fOxygen supply figures shown do
Table 1-5.
Parameter
No. of Plants
Municipal
Industrial
Total
Design Flow (mgd)
Municipal
Industrial
Total
02 Supply Capacity (tons/day)
Municipal
Industrial
Total
Plants Plants
Operating Under Being
Plants Construction Designed
26 49 41
24 17
50 66 41
584.5 2302 2647.3
135.5 191.5
720.0 2493.5 2647.3
477.7 3126.5 3794
389 426.5
866.7 35530 3794
not include data for Japanese plants.
USA Oxygen Plant Status — June 1976
Plants Plants
Operating Under Being
Plants Construction Designed
21 46 41
14 11
35 57 41
570.3 2172.8 2647.3
94.3 166.8
664.6 2339.6 2647.3
467.7 2944.5 3794
389 383.8
856.7 3328.3 3794
Total
116
41
157
5533.8
327.0
5860.8
7398.2
851.5
8249.7
Total
108
25
133
5390.4
261.1
5651.5
7206.2
772.8
7979.0
Table 1-6. Breakdown of Oxygen Plants by Country — June 1976
No. of Plants
Under Being
Country Operating Construction Designed
1. USA
2. Japan
3. Canada
4. Mexico
5. England
6. Germany
7. Denmark
8. Switzerland
9. Belgium
Total
35 57 41
14 3
1
1
1
1
1
1
1
50 66 41
Total
133
17
1
1
1
1
1
1
1
157
-------
Cryogenic oxygen gas generators are sold by several firms in the United States, whereas Union
Carbide is the only known U.S. manufacturer of pressure swing adsorption (PSA) oxygen gas gen-
erators. The break-even range determined by Union Carbide for these two oxygen supply systems
is approximately 20-25 tons/day (18-23 metric tons/day). Below this range, it is more cost effec-
tive to use PSA generators; above this range, cryogenic generators are more cost effective. Other
manufacturers have developed mini-cryogenic oxygen generators to compete for the lower tonnage
plants. On-site cryogenic or PSA gas generation was selected for 80 percent of the 99 oxygen-
activated sludge plants with defined methods of oxygen supply, as of June 1976. The average
capacities for these 79 supply systems are 92 tons/day (83 metric tons/day) for the cryogenic
units and 16.2 tons/day (14.8 metric tons/day) for the PSA units.
Table 1-7. Summary of Oxygen Systems — June 1976
Parameter
Operating
Plants
Plants
Under
Construction
Total
Reactor Type (No.)
Covered Reactor 48
Open Reactor 2
Total 50
O2 Dissolution System Type (No.)
Covered -Surface Aerators 44
Covered - Submerged Turbines 4
Covered - Combination of Aerators and Turbines 0
Open - Rotating Active Diffusers 2
Open - Fixed Active Diffusers _Q_
Total 50
02 Supply System Type (No.)
On-Site Cryogenic Generation 7
On-Site PSA Generation 15
On-Site Liquid Storage and Vaporization 9
Off-Site Pipeline Transport 5
Unknown* 14
Total 50
O2 Supply System Capacity (ton/day)
On-Site Cryogenic Generation 407
On-Site PSA Generation 254
On-Site Liquid Storage and Vaporization 27.8
Off-Site Pipeline Transport 178
Total 866.8
63
_3_
66
59
3
1t
2
1
66
31
26
2
4
3
66
3086.8
413.5
4.5
84.2
3589.0
111
5
116
103
7
1
4
1
116
38
41
11
9
17
116
3493.8
667.5
32.3
262.2
4455.8
O2 Dissolution System Design Flow (mgd)
Covered - Surface Aerators
Covered - Submerged Turbines
Covered - Combination of Aerators and Turbines
Open - Rotating Active Diffusers
Open - Fixed Active Diffusers
Total
286
423.8
0
10.2
0
720.0
1526
345
600f
21.5
1
2493.5
1812
768.8
600
31.7
1
3213.5
tThe oxygen dissolution system for Detroit's second-phase construction consists of submerged
turbines in the lead stages and surface aerators in the rear stages.
*Data unavailable for Japanese oxygen supply systems.
-------
Pipeline transport of off-site generated oxygen gas to an oxygenation wastewater treatment
plant can be an economical choice of oxygen supply if the logistics are reasonable and if the off-
site facility (e.g., a steel production plant) has extra generation capacity. This method of oxygen
supply accounts for 9 percent of the defined supply systems and 6 percent of the June 1976 "oper-
ating" and "under construction" capacity. On-site storage and vaporization of trucked-in liquid
oxygen, because of its high unit cost, is generally confined to requirements of 5 tons/day (4.5
metric tons/day), or less. The oxygen consumption of the 11 such systems documented in Table
1-7 is expected to average 2.9 tons/day (2.6 metric tons/day). This amounts to only 0.7 percent
of the defined oxygen supply capacity.
Oxygen plants treating or scheduled to treat industrial wastewaters are broken down by in-
dustrial application in Table 1-8. Eight major categories are represented in the "operating" and
"under construction" classifications. The pulp and paper industry leads the list with nearly one-
half of the total plants and over three-fourths of the total design flow. The next most frequent
users to date have been the petrochemical and chemical industries. Inasmuch as oxygenation
technology is well suited to satisfying the high oxygen demand associated with many industrial
wastewaters, continuing rapid growth in the oxygen industrial market is anticipated for years
to come.
Table 1-8. Breakdown of Oxygen Plants by Industrial Application — June 1976
Operating
Plants
Industrial
Application
1. Chemicals
2. Dyestuffs
3. Food Processing
4. Petrochemical
5. Pharmaceutical
6. Pulp & Paper
7. Steel
8. Synthetic Rubber
Total
No.
of
Plants
4
0
1
5
2
11
0
1
24
Design
Flow
(mgd)
10.9
0
1
9.9
1.7
111.2
0
0.8
135.5
Plants
Under
Construction
No.
of
Plants
3
1
1
3
0
8
1
0
17
Design
Flow
(mgd)
15.2
3.1
1.8
15.0
0
142.7
13.7
0
191.5
Total
No.
of
Plants
7
1
2
8
2
19
1
1
41
Design
Flow
(mgd)
26.1
3.1
2.8
24.9
1.7
253.9
13.7
0.8
327.0
10
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Chapter 2
DESCRIPTION OF SECOND GENERATION
OPEN REACTOR OXYGEN SYSTEM (MAROX)
The covered reactor oxygen system, including both the surface aerator and submerged turbine
alternatives, has been described previously in the Proceedings of the Second U.S.-Japan Conference
on Sewage Treatment Technology (2) and elsewhere (3). A description of the first generation fixed
active diffuser (FAD) version of the open reactor oxygenation system was also provided in these
documents. It is not deemed necessary to reiterate those descriptions here; however, certain charac-
teristics of the covered reactor systems and the FAD open reactor system are compared with the
second generation open reactor option, described below.
A section view of the key element (the rotating active diffuser (RAD)) is shown in Figure
2-1. As indicated, the basic RAD consists of a 7-ft (2.1-m) diameter submerged rotating plate
mounted to the bottom of a 6-5/8-inch (16.8-cm) diameter hollow shaft approximately 3 ft
(0.9 m) above the aeration tank floor. A 7-1/2-inch (19.1-cm) wide ceramic diffusion medium
is inserted into preformed openings top and bottom around the periphery of the plate, forming
two circular diffusion bands parallel to the outer tapered edge. Approximate 28-inch (71-cm)
diameter radial impellers mounted to the top and bottom of the plate provide essential mixing
of oxygen, substrate, and biomass. An optional surface impeller can be installed to aid in foam
breakup, if desired. The relatively low design rotational velocity of 75-85 rpm is achieved with
a constant speed motor and an appropriate gear reduction unit. The composite submerged
assembly is illustrated in a cutaway perspective view in Figure 2-2.
A functional flow diagram for a typical MAROX system employing RAD's for oxygen trans-
fer is presented in Figure 2-3. The primary oxygen supply (shown as a cryogenic generator) is sup-
plemented by a liquid oxygen reserve supply and accompanying vaporizer. With a cryogenic gen-
erator, unlike a PSA generator, losses occuring from the liquid oxygen backup tank, either through
usage or evaporation, can be replenished directly from the primary supply source.
Oxygen gas from the supply system is pressurized to 30 psig (2.1 kfg/sq cm) with a sepa-
rate compressor (not shown in Figure 2-3) and fed down through the hollow RAD shafts and
then radially outward through small ducts located inside the diffuser plate to the ceramic medi-
um. As oxygen gas emerges from the upper and lower diffusion bands, the rotational shear
created by centrifugal force forms ultra small bubbles in the 50-100 micron range which do not
coalesce as they move outward and pass over the outside tapered edge of the diffuser plate.
The primary function of the tapered edge is to prevent turbulence which could induce bubble
coalescence. The resulting micron bubble dispersion resembles a mist from which oxygen is
rapidly and efficiently dissolved in the mixed liquor. The oxygen transfer rate obtained with
bubbles of this minute size is sufficiently high to reportedly sustain an oxygen utilization ef-
ficiency greater than 90 percent in conventional depth uncovered aeration tanks (4).
11
-------
STANDARD
RAILING
FLEXIBLE HOSE
ROTATING GAS SEAL
MOTOR
I GAS SUPPLY LINE
STANCHION
GEAR REDUCER c
WALKWAY AND TOP OF COPING
WATER LEVEL
SURFACE IMPELLER
•III II
i
—-6-5/8" DIA.
HOLLOW SHAFT
MIXING IMPELLERS
Illlli II
Dili Illl HIM. II
— T rr
HI A 'm-
DIFFL
MEDI
TANK FLOOR
Figure 2-1. Section view of rotating active diffuser and drive assembly
12
-------
MIXING
IMPELLERS
(TOP & BOTTOM)
DIFFUSION
MEDIUM
(TOP AND BOTTOM)
Figure 2-2. Perspective view of submerged rotating active diffuser showing gas flow and
bubble formation.
PRIMARY
OXYGEN
SUPPLY
CONTROL
PANEL
CONTROL LINE
OXYGEN SUPPLY
LOX STORAGE
(STAND-BY)
NTRO
j
VALVE
.AU
T—
TROL
ALVE
. --t
INFLUENT f—
WASTE WATER *-d
RETURN-J
SLUDGE —
'•t|k
: P ~1
.-'•
'/
I
L i
•y T I SPEED
^ . ,1 REDUCER
f
1
^
"N^
J
i —
f i
•f— — — —
—
f ^
r
lf
hoo
ANALYZER [^y
DO PROBE
^ ^
*\ /* -^ r M ^ x "S
*-
AERATION
TANK FLOOR
OVERFLOW WEIR
TYPICAL
OPEN BASIN
LIQUOR
TO FINAL
CLARIFIER
Figure 2-3. Functions flow diagram of typical system employing rotating active diffusers.
13
-------
A dissolved oxygen (DO) feedback system is used to control the oxygen feed rate to the
RAD's. The control system, consisting of one or more DO probes, analyzers, control valves, and
electronic controllers, automatically maintains the mixed liquor DO concentration at a predetermin-
ed setpoint, within the tolerance range of the equipment. A one-module control system, i.e., one
probe, analyzer, control valve, and controller each, is shown controlling the oxygen feed rate to
both diffusers in Figure 3. In a longer tank requiring 10-20 RAD's, multiple control modules would
be necessary with each module controlling the feed rate to a bank of 3-5 diffusers.
The lack of necessity for a tank cover avoids the sealing problems that must be considered with
the covered reactor systems. Although most covered reactor systems designed to date have included
staging baffles, they are not essential. Both the open and covered reactor alternatives can be de-
signed compatibly with any of the commonly used activated sludge flow regimes. Covered reactor
systems are, however, more naturally adapted to the conventional plug flow regime. Where conven-
tional activated sludge treatment is the flow regime of choice, the staged configuration more nearly
approximates ideal plug flow and, other factors being equal, would be expected to deliver an
effluent with a slightly lower soluble BOD than an unstaged system.
Other features distinguishing the open and covered reactor approaches from each other are:
1. The type of oxygen feed control systems. As mentioned previously, open reactor systems
utilize a DO based oxygen feed control system. The covered reactor systems control oxygen feed
rate by maintaining a predetermined gas pressure in the first-stage head space.
2. Freeboard requirements. Covered reactors require more freeboard than open reactors.
The greater freeboard is needed to provide adequate gas space for the umbrella throw pattern of
the surface aerators normally employed in covered reactor designs. Utilization of submerged oxygen
dissolution equipment obviates the necessity for as large a freeboard with the open reactor system.
3. Carbon dioxide buildup. It is anticipated that open reactor systems will be less subject to
carbon dioxide buildup and attendant pH depression than systems due to the absence of a tank
cover. The degree to which cell respiration by-products are vented from the open reactor will
depend primarily on surface turbulence levels and the thickness of foam buildup, if any, on the
aerator surface.
4. Hydrocarbon buildup. The absence of a tank cover virtually eliminates the possibility
of accumulating an explosive concentration of volatile hydrocarbons over the aerator liquid sur-
face. It is assumed, therefore, that safety precautionary measures could be less extensive with open
systems than with covered reactor systems.
5. Oxygen feed pressure to the oxygen dissolution systems. The nominal pressure of oxygen
gas leaving cryogenic and PSA generators is 3-5 psig (0.21-0.35 kgf/sq cm). This is more than suffi-
cient to satisfy line and entrance losses to a covered reactor and maintain a pressure of 1-3 inches
(2.5-7.5 cm) of water in the first-stage vapor space. Conversely, head loss through either of the open
reactor diffusers is substantial, requiring an additional compressor to pressurize generator output to
30 psig (2.1 kgf/sq cm).
In comparing the two open reactor options, the several inherent advantages of the RAD system
over the FAD system are expected to produce a pronounced preference for the RAD alternative.
These advantages include:
— no requirement for prescreening of aerator influent,
— no requirement for pumping mixed liquor through the diffusers to create the necessary
shear to produce micron size bubbles,
14
-------
— reduced oxygen dissolution power requirements,
— simplified installation, and
— less maintenance.
METRO DENVER DEMONSTRATION PROJECT
In June 1975, the U.S. Environmental Protection Agency (EPA) awarded a $200,000 demon-
stration grant to Metropolitan Denver (Colorado) Sewage Disposal District No. 1 to evaluate the
MAROX system. The remainder of the estimated total project cost of $605,000 is being shared by
the District and FMC. The EPA Grant No. is S803910.
The evaluation is being conducted in a segment of Metro Denver's existing air-activated sludge
plant. The plant's secondary system consists of thirty-six 210-ft (64-m) long, 670,000-gal (2536-cu
m) aeration bays and twelve 130-ft (39.6-m) diameter clarifiers. Each of the clarifiers is mated with
three aeration bays operated in series to form 12 parallel secondary trains. Several of the bays have,
on occasion, been utilized for aerobic stabilization of waste activated sludge. Sludge is re-cycled
separately for each quadrant of the plant, i.e., settled sludge from the three clarifiers in any given
quadrant is transferred to a common collection well from where it is returned for distribution
among the three aeration trains in that quadrant.
Approximately two-thirds of the average influent flow of 140 mgd (6.1 cu m/sec) receives
primary sedimentation before it reaches the plant; the other third is primary settled on site. A new
72 mgd (3.2 cu m/sec) UNOX facility will divert a significant fraction of the primary effluent flow
from the existing overloaded air-activated sludge plant.
Prior to grant award, it was mutually decided that the large-scale MAROX system to be evalu-
ated by the District would employ RAD's rather than the older FAD's used in previous pilot-scale
studies at Metro Denver and on a previous EPA supported grant project at the Englewood, Colorado,
wastewater treatment plant (2) (3). Thirteen RAD's were installed in the first bay of aeration train
No. 11 of the existing Metro air plant. The other two bays of this train have been taken out of
service for the duration of the project. Required hydraulic modifcations included the installation of
a pipe to transfer mixed liquor from the end of the first bay to clarifier No. 11 and separate return
and waste sludge lines and pumps. The latter step was taken to isolate MAROX sludge from the
recycle sludge of the two remaining operating air trains (Nos. 7 and 9) of the plant's northeast
quadrant. A liquid oxygen storage tank and vaporizer were installed adjacent to the converted
oxygen test bay. During the first portion of the evaluation, trucked-in liquid oxygen is being used
for oxygen supply. However, the two 40-ton/day (36.3-metric ton&day) cryogenic oxygen gas
generators that will serve the new Metro Denver UNOX treatment plant will have excess capacity
initially. For economic reasons, consideration is being given to utilizing the excess capacity for
supplying oxygen to the demonstration project once shake-down of the cryogenic units is complete.
If this action is taken, a compressor will have to be installed to raise generator output pressure to a
level compatible with RAD operation. A process schematic of the Metro Denver test system is given
in Figure 2-4. Dimensioned plan and section views are shown in Figure 2-5.
As indicated in Figure 2-5, the RAD's are located on 21-ft (6.4-m) centers. Six of the 13 dif-
fusers were installed in sets of two in the first quarter of the tank where oxygen demand is greatest.
The remaining seven diffusers are located in tandem on the longitudinal center line of the aeration
tank. The first 11 RAD's are driven by 10-hp (7.5-kw) motors and rotate after gear reduction at
85 rpm The motors for the last two RAD's are 7-1/2 hp-(5.6-kw) units. The rotational speeds of
the twelfth and thirteenth RAD's are 80 and 76 rpm, respectively. The oxygen dissolution capa-
15
-------
bility of the diffusers is rated at 1500 Ib/day (680 kg/day) each in the District's wastewater for a
total system capacity of 9.75 tons/day (8.85 metric tons/day). Previous proprietary tests indi-
cated these diffusers can be operated up to 33 percent over their rated capacity without significant-
ly affecting oxygen transfer efficiency. On this basis, assuming an average BOD 5 removal of 140
mg/1 and an oxygen requirement of 1.3 Ib 02/lb BODs removed (1.3 kg/kg), the maximum sus-
tained flow which can be handled by this oxygen dissolution equipment is roughly 17 mgd (0.74
cu m/sec).
Three DO probes and control systems are employed to control oxygen feed to the Metro
Denver test bay. One system controls the feed rate to the first six diffusers, the second to the
middle four diffusers, and the third to the last three diffusers. Based on mutual agreement, an initial
DO setpoint of 3.0 mg/1 was selected. During the first month following startup, the oxygen control
equipment exhibited a variance range of ±0.7 mg/1 from the desired setpoint.
DISSOLVED
OXYGEN PROBES
INFLUENT
WASTEWATER
WASTE .
SLUDGE
j SLUDGE
I DRAW-OFF RETURN ACTIVATED SLUDGE
Figure 2-4. Process schematic of Metro Denver test system.
16
-------
EFFLUENT TO
SECONDARY
CLARIFIER
—• r
-f— +— 4
^ LIQUID OXYGEN SUPPLY
-CONTROL VALVE
2" DIA
1"
1 '»* * * * *
I 1-1/2"
I *
I 1-1/2"
+ * * + * t,
OXYGEN SUPPLY TO INDIVIDUAL DIFFUSERS
DISSOLVED OXYGEN PROBE r*A
TOTAL THREE FURNISHED
MOUNTED ON THE BASIN HAND RAIL :
JL JL JL Jl JL JIL-JT T 1
ill ill ¥ ill III ill —Hlb- -(lib- -dl
_ __ ROTATING DIFFUSERS_
9 EQUAL SPACES AT 21 '-0" = 189'-0"-
TOTAL 13 DIFFUSERS
210'-0" LENGTH
INFLUENT
FROM PRIMARY
SETTLING
TANK
RETURN SLUDGE FROM SECONDARY CLARIFIER
LIST OF EQUIPMENT FURNISHED BY FMC
• BRIDGES, BRIDGE SUPPORTS, HANDRAILS
• DIFFUSERS WITH DRIVE UNITS
• LIQUID OXYGEN STORAGE TANK
•VAPORIZER
• OXYGEN SUPPLY
• CONTROL PANEL (NOT SHOWN)
•CONTROL INSTRUMENTATION (NOT SHOWN)
SECTION A-A
V-6"
Figure 2-5. Dimensioned plan and section views of Metro Denver test system
The RAD's and RAD drives are supported from metal bridges which span the aeration test
bay, as illustrated in Figure 2-5. The bridges in turn are supported by stanchions (not shown in
Figure 2-5) running to the tank floor. The bridges were tied with minimal defacing into the side
walls of the test bay to prevent lateral movement. Following delivery of the key components of
the oxygen supply and dissolution systems to the project site, the entire installation including pip-
ing modifications was completed in six weeks. Due in part to the short period in which its system
components can be installed and the minimum structural modifications required, the upgrading of
existing air-activated sludge plants as exemplified by the Metro Denver demonstration project is
expected to become an important application.
From the section view of Figure 2-5, it can be seen that surface impellers were not provided
with the RAD's. The District has experienced a float building of relatively high solids concentra-
tion (2-3 percent TSS) on the mixed liquor surface. Under other circumstances and with the prop-
er removal equipment, this float would constitute a potentially attractive source from which to
waste excess sludge at a substantially higher solids concentration than available in secondary clari-
fier underflow. Since the District is not equipped to waste sludge in this manner, the presence of
the float represents an operational and esthetic liability. To overcome this problem, installation of
an aeration test bay overflow weir, similar to the one shown in Figure 2-3, is under consideration.
The weir would replace the present submerged orifice through which the mixed liquor now exits
the aeration bay. Utilization of an overflow weir would promote continuous transfer of floated
solids to the secondary clarifier before they could accumulate on the liquid surface. Another
float avoidance technique being evaluated is the use of one or more down draft propeller pumps
to recirculate floated solids back into the mixed liquor. For long term operation, the overflow
17
-------
weir option is believed to be a more positive and cost-effective method than either surface im-
pellers on the RAD shifts or down draft propeller pumps. For expediency on this finite length
demonstration project, however, the down draft propeller pump technique may be selected,
even though it would add 6-12 percent to oxygen dissolution system power requirements.
The major objective of the project from the District's standpoint is to determine the technical
feasibility and attendant costs of converting its existing air-activated sludge plant to a higher capac-
ity (i.e., two to three times higher) open reactor, oxygen-activated sludge system. If successful, the
District could potentially avert another major secondary plant expansion for the foreseeable future,
with the exception of the additional clarifiers which would be needed to handle increases in influent
flow. EPA's primary project objectives are: (1) to demonstrate at a representative field scale an
alternative oxygenation concept which has been extensively and successfully evaluated at pilot
scale and (2) to define reliable design criteria, operating conditions and costs, and performance
expectation for a system embodying that concept for use by the engineering community.
Equipment installation and piping modifications were completed in early May 1976. The re-
mainder of the month was devoted to facility shakedown and adjustments. June was utilized as a
process start-up period for training operators and refining a data logging and retrival system. The
evaluation program was initiated on July 1, 1976. The five phases and corresponding dates of the
evaluation program are described below:
Phase I, July 1976,
Constant flow @ 2 mgd (0.39 cu m/sec); warm wastewater temperatures; one clarifier only in
use
Phase II, August-September 1976,
Diurnally varied flow @ 7 to 14 mgd (0.31 to 0.61 cu m/sec); warm wastewater temperatures;
second clarifier available, if necessary
Phase III, October 1976,
Constant flow @ 2 mgd (0.34 cu m/sec); cool wastewater temperatures; one clarifier only in
use
Phase IV, November-December 1976,
Diurnally varied flow @ 7 to 14 mgd (0.31 to 0.61 cu m/sec); cool wastewater temperatures;
second clarifier available, if necessary
Phase V, January-April 1977,
Constant flow increased in increments to failure; cool wastewater temperatures; two clarifiers
in use
Anticipated operating conditions are not documented here for each planned phase because of
the variability that will be introduced by diurnal flow. However, for reference purposes, baseline
operating conditions are summarized below for the 9-mgd (0.4 cu m/sec) constant flow phases,
assuming an average primary effluent BODs concentration of 140 mg/1, a sludge return rate equal
to 40 percent of the influent flow rate, and average mixed liquor suspended solids (MLSS) and
mixed liquor voltaile suspended solids (MLVSS) concentrations of 4000 and 3200 mg/1, respec-
tively:
Nominal Aeration Time (based on Q) = 1.79 hr
Actual Aeration Time (based on Q + R) = 1.28 hr
Food to Microorganism (F/M) Loading = 0.59 Ib BODs applied/day/lb MLVSS under aeration
(0.59 kg/day/kg)
Volumetric Organic Loading = 1 17 lb BODs applied/day/1000 cu ft aerator volume
(1503 kg/day/cum)
18
-------
Secondary Clarifier Overflow Rate (based on total surface area) = 678 gpd/sq ft
(27.6 cu m/day/sq m)
Secondary Clarifier Overflow Rate (based on useful surface area; excludes effluent launder area)
= 746 gpd/sq ft (30.4 cu m/day/sq m)
Secondary Clarifier Mass Loading (based on floor area) = 31.7 Ib MLSS/day/sq ft
(155 kg/day/sq m)
Average operating and performance data for the startup month of June 1976 are presented in
Table 9. The average secondary effluent suspended solids (TSS) concentration of 30 mg/1 is only
marginally acceptable. Daily log sheets reveal, however, that this effluent parameter exhibited a
steadily decreasing concentration trend throughout the 30-day period as operators became more
familiar with system operation and sludge inventory management. Effluent TSS for the first 12
days of July averaged 20 mg/1, a 33 percent decrease from June. The seven-day/week data collec-
tion program depicted in Table 2-1 will be used, along with several additional tests not conducted in
the startup month, throughout the planned evaluation studies. One of these additional tests will be
the periodic determination of oxygen utilization efficiency. This will be accomplished with the aid
of a 6-ft x 6-ft (1.8-m x 1.8-m) floating dome. Off gases from a 36-sq ft (3.34-sq m) area of tank
surface will be collected inside the dome and funneled through a gas flow and composition monitor-
ing station. The tent will be moved to different sections of the aeration test bay to arrive at a com-
posite or average utilization efficiency.
Caution should be exercised in extrapolating the sludge production and oxygen supply rates
given in Table 2-1. These values are for one month of operation only and were generated immedi-
ately following a period of operator familiarization with a new process. A better perspective of the
relationship of these important parameters to organic loading will be gained from an evaluation of
all the data at the end of the project.
19
-------
Table 2-1. June 1976 Average Operating and Performance Data for
Metro Denver Open Reactor Oxygenatlon Project
Influent Flow 9.5 mgd
Return Sludge Flow 3.8 mgd
Return Sludge Flow/Influent Flow 40%
Pri. Eff. BODs 126 mg/1
Sec. Eff. BODs 19 mg/1
BODs Removed Across Secondary 85%
Pri. Eff. TOG 87 mg/1
Sec. Eff. TOG 29 mg/1
TOG Removed Across Secondary 67%
Pri. Eff. TSS 88 mg/1
Sec. Eff. TSS 30 mg/1
TSS Removed Across Secondary 66%
MLSS 3050 mg/1
MLVSS 2610 mg/1 (volatiile fraction = 85.6%)
Mixed Liquor DO 2.7 mg/1
Mixed Liquor! Temperature 20° C
Return Sludge TSS 10,970 mg/1
Return Sludge VSS 9120 mg/1 (volatile fraction = 83.1%)
Depth to Clarifier Sludge Blanket 7.5 ft
Nominal Aeration Time (based on Q) 1.69 hr
Actual Aeration Time (based on Q + R) 1.21 hr
F/M Loading 0.68 Ib BODs applied/day/lb
MLVSS under aeration
Volumetric Organic Loading 111 Ib BODs applied/day/1000 cu ft
aerator volume
Secondary Clarifier Overflow Rate
(based on total surface area) 716 gpd/sq ft
Secondary Clarifier Overflow Rate
(based on useful surface area;
excludes effluent launder area) 787 gpd/sq ft
Secondary Clarifier Mass Loading
(based on floor area) 25.5 Ib MLSS/day/sq ft
Waste Activated Sludge Mass 5060 Ib/day
Sludge Production Rate (based on waste sludge TSS only) 0.60 Ib TSS/lb BODs removed
Sludge Production Rate (based on
waste sludge & sec. eff. TSS) 0.88 Ib TSS/lb BODs removed
Sludge Retention Time (SRT) 2.3 Ib MLSS under aeration/ (Ib waste
sludge TSS + sec. eff. TSS
lost)/day = 2.3 days
RAD Power Draw 109 hp
Oxygen Supplied 11,363 Ib O2/day
Oxygen Supply Rate (based on load) 1.14 Ib O2/lb BODs applied
Oxygen Supply Rate (based on removal) 1.34 Ib O2/lb BODs removed
20
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Chapter 3
CASE HISTORIES
Operating and performance data and case history summaries are presented below for 11
oxygen-activated sludge plants. All 11 plants are documented in the listing of operating facilities
provided in Table 1 -1.
The case histories were selected to illustrate a variety of process applications, system compon-
ent configurations, and plant sizes. Eight of the selected plants treat municipal wastewaters: three
are strictly industrial applications. Several of the municipal installations receive a significant frac-
tion of their incoming loads from industrial sources. The reactor designs for these plants represent
a variety of configurations including both rectangular-stage systems and systems incorporating cir-
cular and arcuate stages within larger self-contained circular tanks.
In addition to operating and performance data, a flow diagram is presented for each case his-
tory along with pertinent background information, where known, leading to the selection of an
oxygen system.
Noteworthy start-up, operating, and maintenance difficulties encountered are discussed.
Secondary system components and any flow routing peculiarities are described briefly. Data avail-
able to the writer for summarization herein varied from one month's results at several plants to
more than two years' results at another location.
Decatur, Illinois
Prior to the recent addition of a UNOX system, the Sanitary District of Decatur's wastewater
treatment plant consisted of two rectangular primary clarifiers, six Imhoff tanks, 12 air aeration
days, three secondary clarifiers, two trickling filters, one primary anaerobic digester, one secondary
digester, one supernatant holding tank, and tertiary and sludge lagoons. Six of the existing air
aeration bays are of 1935 vintage; the other six are larger and were installed in 1965.
In July 1975, the liquid portion of a comprehensive plant upgrading program was completed.
The heart of this upgrading effort was the conversion of three of the 1965 air aeration bays to oxy-
gen service. The walls of these bays were extended upwards 4 ft (1.2 m) and the bays covered to
provide the needed vapor space to satisfactorily control oxygen feed and interstage gas transport.
The remaining nine air aeration bays have been combined into an integrated system to -operate in
parallel with the oxygen unit in either the conventional mode or as a modified contact stabiliza-
tion process. The nine bays are shown schematically in the flow diagram of Figure 3-1 as two
tanks, one representing the six older 1935 bays, the other the three newer 1965 bays.
Coinciding with the modifications to implement oxygen-activated sludge treatment, three new
primary clarifiers and four new secondary clarifiers were constructed. Two of the three new pri-
maries have 100-ft (30.5-m) diameters and are in use continuously. The third new primary has a
diameter of 130 ft (39.6 m) and is only used during severe storms with the overflow discharged
directly to the receiving river following chlorination. The new secondary clarifiers are mated with
the UNOX system, the old secondaries with the revamped air aeration facilities. The diameter and
21
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PSA GENERATOR 17 TPD
I
t
LOX
STORA(
I
3E
I
I I
1
I I I
BAR SCREEN
-DEGRITTERS
H PRIMARY CLARIFIERS
BYPASS PEAK FLOWS
INFLUENT
TO LANDFILL
WASTE SLUDGE
PRIMARY
SLUDGE
AIR REACTOR
UNOX REACTOR
SUPER-
NATANT
HOLDING
TANK
RECYCLE
SLUDGE
EFFLUENTi
UNOX
CLARIFIERS
(4)
ANAEROBIC
AIR CLARIFIERS
TO LANDFILL
DIGESTERS
WASTE SLUDGE
Figure 3-1. Flow diagram of Decatur, Illinois wastewater treatment plant.
22
-------
side water depth (SWD) of the new secondaries are 100 ft (30.5 m) and 12.5 ft (3.8 m), respec-
tively. The old trickling filters (not shown in Figure 3-1) were abandoned in September 1975. The
old rectangular primary clarifiers (also not shown in Figure 3-1) have been placed on standby service.
A program to upgrade the sludge handling portion of the plant was completed in December
1976. The old supernatant holding tank and old secondary digester were converted to heated pri-
mary anaerobic digesters to join the one existing primary digester. Supernatant is now returned
directly to the plant headworks. Five of the existing six Imhoff tanks (omitted from Figure 3-1)
were outfitted with covers to operate as non-heated secondary digesters. The sixth Imhoff tank
remains uncovered and serves as a holding tank for both oxygen and air waste activated sludges
prior to separate thickening in a new concentrator. Waste sludge was returned to the primaries for
thickening before digestion.
Each of the three oxygen trains is divided into four stages. The overall dimensions of the oxy-
gen reactor are 148 ft long x 77 ft wide x 14 ft SWD (45 m x 23.5 m x 4.3 m) with a freeboard of
4 ft (1.2 m). The oxygen dissolution system consists of surface aerators combined with bottom
propellers for additional mixing. The PSA oxygen generation unit has a design output capacity of
17 tons/day (15.4 metric tons/day). The storage capacity of the backup liquid oxygen supply tank
is 43 tons (39 metric tons).
On the average, 55 to 60 percent of the incoming organic load is from industrial sources, pri-
marily corn and soybean processing. Some of the industrial contributors have their own treatment
facilities which discharge effluent into the Decatur sewer system. The particular mixture of domes-
tic, industrial, and partially treated wastes received at the Decatur plant is conducive to the forma-
tion of a poor settling filamentous sludge. Filamentous conditions have been a historical problem
with and continue to seriously plague the air aerated trains. According to plant personnel, fila-
mentous infestation is much less prevalent in the oxygen sludge, but is present in sufficient quanti-
ties that a substantially less dense settled sludge is produced than predicted. Even so, oxygen
clarifier underflow concentrations range from 70-100 percent higher than comparable data for
settled air sludge.
The inability to thicken oxygen sludge during clarification to the degree planned has resulted
in lower MLSS and higher F/M operating conditions than designed for. These conditions have appar-
ently not adversely affected effluent quality which remained good throughout the first year of
operation, as indicated in Table 3-1. The somewhat higher effluent suspended solids value shown
for February corresponded to an average influent flow equal to 115 percent of design. The ef-
fluent data given in Table 3-1 represented UNOX system effluent quality prior to mixing with
air system effluent or subsequent treatment in the tertiary lagoons.
Recent communication with the assistant plant manager elicited the following observations
on his part:
1. The oxygen system has consistently outperformed the air system by a wide margin,
despite treating approximately twice as much flow in a substantially smaller reactor volume.
2. The oxygen system has exhibited excellent day-to-day process reliability and is generally
capable of recovering from slug loading upsets within 24 hours.
3. Oxygen dissolution and supply systems require more operator attention than convention-
al air processes, primarily because of the greater amount of instrumentation involved. Several
equipment malfunctions to date have been beyond the ability of the plant operating staff to correct
and have required attention on the part of the vendor.
23
-------
4. Several PSA compressor outages are experienced during early operations due to an im-
proper inner cooling system. The cooling system was eventually redesigned and rebuilt and is now
performing satisfactorily.
The upgrading modifications implemented at Decatur have resulted in an increase in plant
capacity from 20 mgd (0.9 cu m/sec) to 25 mgd (1.1 cu m/sec) and a substantial improvement in
total plant performance. Two-thirds of the upgraded 25 mgd (1.1 cu m/sec) capacity is assigned
to the new oxygen system, one-third to the existing air system.
Table 3-1. Operating and Performance Data for Decatur, Illinois Oxygen System
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BOD5/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BODs (mg/1)
TSS (mg/1)
Secondary Effluent BODs (mg/1)
TSS (mg/1)
Design
17.7
1.6
0.62
560
5500
1.9
188
138
20
25
Aug.
1975
14.4
1.97
1.10
456
2700
0.55
157
139
9
22
Operation
Feb.
1976
20.4
1.39
1.47
645
3300
0.93
129
138
15
36
July
1976
14.1
2.01
0.91
446
2600
0.87
98
99
10
20
Detroit (# 1), Michigan
Initial planning for expansion to secondary treatment at Detroit called for the installation of a
1200 mgd (52.6 cu m/sec) air-activated sludge facility to be completed over a four-phase construc-
tion period spanning approximately ten years. Two 150-mgd (6.6-cu m/sec) air train modules were
to be installed during each construction phase, yielding an eventual total of eight modules.
Coinciding with Detroit's planning program, the use of oxygen in the activated sludge process
was being investigated in a federally supported research project at Batavia, New York (1) (2) (3).
Based primarily on promising results emanating from this project, Detroit became interested in
utilizing oxygen in its own treatment situation. The City made a decision in 1969 to modify its first
construction phase to include one 150-mgd (6.6-cu m/sec) air module and one 300-mgd (13.1-cu m/
sec) UNOX module. The reactor tanks for both systems were designed with identical outside dimen-
sions, meaning that the aeration detention time of the oxygen system was to be one-half of that of
the air system. The high-rate treatment potential of the oxygenation process was of utmost import-
ance to the City because of a serious land shortage problem.
The construction contract awarded by the City included process guarantee requirements for
the system in the areas of effluent quality, power consumption, and oxygen consumption. The effi-
cacy of the UNOX and air systems was to be compared in parallel test runs. Depending on the re-
sults of the tests, the two systems were designed such that the 150-mgd (6.6-cu m/sec) air train
could be readily converted to a 300-mgd (13.1-cu m/sec) oxygen train by the addition of a tank
cover, submerged turbine/sparger units for oxygen dissolution, and three more secondary clarifiers.
With this possibility in mind, the compressors which continuously recirculate gas through the sub-
24
-------
merged turbine/sparger units were double sized to handle 600 mgd (26.3 cu m/sec). If the test re-
sults indicated superior performance by the air train, the City retained the option by virtue of the
identical reactor designs of switching the higher capacity oxygen system to a 150-mgd (6.6-cu m/
sec) air system by removing the tank cover and substituting air draft tubes for the oxygen dissolu-
tion equipment.
CRYOGENIC GENERATOR 180 TPD
LOX
STORAGE
PICKLE LIQUOR
FROM INDUSTRY
RACK
& GRIT
PRIMARY CLARIFIERS
AIR
REACTOR
»_ |SLUDGE__
SLUDGE
THICKENING
INCINERATION1
VACUUM
FILTRATION
SECONDARY
CLARIFIERS
RECYCLE SLUDGE
CHLORINATON-
I
TO LANDFILL
RECYCLE SLUDGE
r
[EFFLJJENT
Figure 3-2. Flow diagram of Detroit, Michigan wastewater treatment plant -
Phase #1 construction.
25
-------
For the test runs, six secondary clarifiers were to be mated with the oxygen reactor, three with
the air reactor. The clarifiers are of unique design with a diameter of 200 ft (61 m), a SWD of 16 ft
(4.9 m), an extremely high average surface overflow rate of 1600 gpd/sq ft (65 cu m/day/sq m),
rapid sludge removal suction pipes, and a peripheral-feed rim-takeoff flow configuration. Although
the oxygen module has been in operation since August 1974, the writer is not aware of the publica-
tion of any officially conducted comparative test results on the two systems to date. Normal start-
up problems and delays in getting nine clarifiers completed reportedly contributed to the delay in
parallel testing. Whether official test data are eventually published or not, it would appear that
Detroit is committed to oxygen use. Two new 300-mgd (13.1-cu m/sec) oxygen modules are now
under construction as part of the City's second-phase construction program. The second-phase
oxygen systems will utilize OASES equipment. If Detroit decides at a future date to convert the air
train installed under first-phase construction to oxygen service, the City will have realized its ulti-
mate goal of 1200 mgd (52.6 cu m/sec) of treatment capacity with four reactor modules instead of
eight. A flow diagram for the first-phase air and oxygen modules is given in Figure 3-2.
The large 30-ft (9.1-m) reactor SWD employed in first-phase construction necessitated the use
of the submerged turbine oxygen dissolution alternative. The overall dimensions of the reactor are
600 ft long x 140 ft wide x 33 ft deep (183 m x 42.7 m x 10.1 m). Oxygen gas is supplied by a
180-ton/day (163-metric ton/day) cryogenic generator. A 900-ton (816-metric ton) liquid oxygen
storage tank provides backup.
Following start-up, it became evident that sufficient detail had not been given to the design of
the submerged turbine assemblies. Propeller failures and gear box problems resulted from inade-
quate materials selection and fabrication. Redesign and partial equipment replacement were neces-
sary to correct the deficiencies. Another problem encountered by the plant staff was obtaining a
tight seal at the joints between the outside edges of the reactor cover and the reactor walls. Despite
experiments with several different sealants and sealing procedures, this situation was only marginal-
ly rectified at the time of this writing. Cryogenic generator performance has been very satisfactory
with minimal downtime. During the first 550 days of operation, less than 2.5 percent scheduled and
0.4 percent unscheduled outages were experienced.
Average operating and performance data for the UNOX system are documented in Table 3-2
for September 1975 and a 1-1/2 month period in the spring of 1976. These data were generated at
constant influent flow. Imposition of diurnal flow variations will be postponed until the remainder
of the secondary treatment trains under construction come on-line. It is obvious that reactor in-
fluent BOD5 concentrations have been considerably lower than expected. The weaker strength
primary effluent is partially attributable to the recent initiation of iron addition to the primary
clarifiers for phophorus removal.
Two major operational problems have surfaces with the secondary clarifiers. One involves achiev-
ing proper peripheral influent distribution to avoid short circuiting of mixed liquor solids directly
up to the rim-takeoff weirs. The other is the extreme difficulty encountered in getting settled sludge
to thicken to acceptable concentrations prior to removal from the clarifiers. The impact of the thin
settled sludge situation is evident in Table 3-2 in low MLSS levels and high F/M loadings. The Detroit
oxygen sludge does have good thickening properties as exemplified by the ability to separately
thicken waste sludge to 4 percent solids in 24 hours without chemical conditioners. In the writer's
opinion, secondary clarifier operational difficulties will continue as long as the clarifiers are sub-
jected to the inordinately high overflow rates currently in use.
26
-------
Table 3-2. Operating and Performance Data for Detroit (#1), Michigan Oxygen System
Operation
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarified Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BOD5 (mg/1)
TSS (mg/1)
Secondary Effluent BODs (mg/1)
TSS (mg/1)
Design
300
1.42
0.47
1600
6250
—
140
150
25
30
1975
302
1.41
0.58
1611
2340
0.66
44
105
6
9
March 29 —
May 9, 1976
299
1.42
1.05
1595
2750
0.85
101
240
17
31
Fairfax County, Virginia
The Westgate plant is one of four municipal wastewater treatment plants operated by Fairfax
County,Virginia. This plant, constructed in 1954, was originally designed to remove 50 percent of
the BOD5 loading from a design flow of 8 mgd (0.35 cu m/sec).
Basic features of the original Westgate facility in sequence consisted of bar screening, commi-
nution, primary clarification, once-through aeration, secondary clarification, and chlorination.
Sludge recycle pumps were not provided. The main treatment basin was divided into two parallel
tanks. Each tank housed primary clarification, aeration and secondary clarification sections sepa-
rated only by baffles. Scraper chains passed along the entire floor length through all the sections of
the tanks. The apparent purpose of the scrapers was to move biological solids and grit settling out
in the secondary clarification zones back to the primary clarification zones where they could be
removed from the system. Although the original plant was not intended to function as an activated
sludge system, it is highly likely that some settled solids were resuspended in the aeration zones dur-
ing scraping transport, thus maintaining a small active biomass population in those zones. The de-
cision to forego installation of the additional clarifier appurtenances, sludge recycle equipment, and
piping which would have permitted operation in a conventional activated sludge mode was neces-
sitated by funding limitations at the time of initial construction.
From 1954 to 1965, plant influent flows increased gradually from 8 mgd (0.35 cu m/sec) to
slightly less than 10 mgd (0.44 cu m/sec). BOD5 and suspended solids removals during this period
averaged approximately 50 and 65 percent, respectively. By 1970 with plant flows having further
increased to approximately 11 mgd (0.48 cu m/sec), BOD5 removal had dropped to 45 percent and
suspended solids removal to 55 percent. In 1970, faced with the choice of either upgrading BOD5
removal efficiency to 80 percent or having a building moratorium placed on the area served by the
plant, the County submitted a report to the State of Virginia recommending that interim upgrad-
ing steps be applied at Westgate pending completion of an expansion program at the nearby Alex-
andria, Virginia plant. At that time, the Westgate facility would cease operations in favor of flow
diversion to Alexandria.
The first interim upgrading approach tried was the addition of ferric chloride to the influent
wastewater at the plant headworks followed by anionic polyelectrolyte addition to the aeration
zones. This technique yielded an average BOD5 removal of 71 percent from July 1970 through
October 1971, somewhat short of 80 percent removal target. The sludge resulting from chemical
addition proved to be more difficult to dewater than that of the original plant.
-------
Laboratory tests indicated that combining powdered activated carbon dosing to the influent
wastewater with the above iron and polyelectrolyte additions could potentially improve BOD5
removal to 75 percent. Full-scale trials with carbon dosing were abandoned in July 1971 after a
short-term run due to erosion and feed control problems. Data generated during the run were incon-
clusive.
During the latter portion of 1970, the County and its engineering consultant concluded that
80 percent interim BOD5 removal could be achieved more cost effectively with a biological treat-
ment system than with a combination of chemical addition procedures. A decision was then made
following technical deliberations to implement biological treatment with an oxygen-activated
sludge process rather than a high-rate air-activated sludge process because of reliability and cost
considerations. A contract was awarded in the spring of 1971 to convert the existing Westgate
plant to an OASES system. A contract period of 210 days was allowed to complete the job.
The upgrading plan developed by the County's engineer consisted of four principal steps:
1. Conversion of the aeration and secondary clarification sections of the existing tanks into
a two-train oxygenation reactor leaving the primary clarification sections intact.
2. Installation of two new secondary clarifiers, each 120 ft (36.6 m) in diameter with a
SWD of 11 ft (3.4 m) and suction lift scraper arms for removing sludge.
3. Installation of waste activated sludge thickening capability in the form of two flotation
thickeners, each having a surface area of 250 sq ft (23.2 sq m).
4. Installation of two 7-mgd (0.31-c m/sec) sludge recycle pumps and separate sludge wast-
ing pumps.
A longitudinal section view of the existing Westgate treatment basin prior to conversion to
an oxygen system is given in Figure 3-3. Some of the modifications required to effect the conver-
sion are noted. These included removal of the air diffusers and downcomer piping, removal of the
baffles between the old aeration and secondary clarification sections, removal of all old effluent
weir sections within the secondary clarification sections proper, removal of the old sludge scrapers
from the aeration and secondary clarification zones, replacment of the baffles separating the pri-
mary clarification and original aeration zones, and relocation of some sludge scraper sprockets to
the primary clarification sections. The converted oxygen reactor was divided into four stages in
each train. The stages comprised in order 22, 44, 23, and 11 percent of the total reactor volume.
Only the first three stages were covered, the last stage being left open to the atmosphere because
of the low oxygen demand which would exist at that point. The gas-tight tank covers and liquid
staging baffles were fabricated from carbon steel and coated with an epoxy-phenolic resin. The over-
all dimensions of the converted oxygen reactor are 138 ft long x 82 ft wide x 12 ft SWD (42 m x
25 m x 3.7 m).
A total of 36 surface aerators with bottom impellers were installed for oxygen dissolution and
mixing. Eight of the aerators (utilized at the front end of the reactor) are 10-hp (7.5-kw) units; the
other 28 have 5-hp (3.7-kw) drives, yielding a total installed nameplate power load of 220 hp
(164 kw). Liquid oxygen is stored on-site and vaporized preceding introduction to the oxygenation
system.
Plant modifications were completed and the converted system started up in November 1971,
making Westgate the oldest full-scale oxygen-activated sludge facility in the world.
A flow diagram of the modified plant is shown in Figure 3-4. Operation of the new flotation
thickeners was terminated after several months. It was found that thickening of excess activated
28
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PRIMARY
CLARIFICATION
BAFFLE REMOVED
OLD EFFLUENT OVERFLOW WEIR
\
n
BAFFLE-*
REPLACED
AIR DIFFUSERS REMOVED
V y
SECTIONS ABANDONED
SECTION CURRENTLY IN USE
SPROCKETS RELOCATED
Figure 3-3. Longitudinal sectional view of pre-modified concrete tank at
Fairfax County (Westgate), Virginia wastewater treatment plant.
SLUDGE STORAGE
TANK
POLYELECTROLYTE
STORAGE AND
ABANDONED
ACTIVATED CARBON
SLURRY
CHLORINE^
CONTROL
LING CHAMBER
VACUUM
FILTER
XXX'
TO DUMPSTER
FERRIC
CHLORIDE
STORAGE
& FEEDING
ADMINISTRATION BLDG.UNDERFLOW
SEDIMENTATION
SLUDGE
DECANT
TANKS
COMMINUTORS
CLARIFIER
OVERFLOW
POLY-
ELECTROLYTE
FLOTATION
THICKENER
CHLORINE
SLUDGE
PUMP
"F" STREET PUMPING STATION
AIR POLYELECTROLYTE
Figure 3-4. Flow diagram of Fairfax County (Westgate), Virginia wastewater treatment plant.
29
-------
sludge beyond that afforded by gravity decant tanks was not needed prior to mixing with primary
sludge and vacuum filtration. The comminutor was also removed from service several months into
the upgraded operation.
Start-up difficulties were minimal and of the type normally associated with "debugging" a new
system A process optimization program was undertaken for the County by Air Products and
Chemicals from late January 1972 to May 1972. The primary purpose of the program was to define
the operating conditions for this first-of-a-kind system which would result in a consistently high
level of plant performance. Operating and performance data are presented in Table 3-3 for the one-
year period of August 1972 through July 1973. As indicated, excellent effluent quality was
achieved, far exceeding the 80 percent BOD5 removal design specification, at an average influent
flow equal to 76 percent of design capacity. Primary influent rather than reactor influent concen-
trations are included in Table 3-3 because representative sampling of primary effluent is not pos-
sible. Little alteration of influent wastewater characteristics is believed to be effected by the pri-
maries due to their short detention time (20-25 minutes).
The Westgate story is a superb example of utilizing existing tankage to the fullest in an up-
grading project intended to simultaneously improve plant performance and increase plant capacity.
It is not known in view of the excellent performance achieved to date whether the upgraded plant
will still be abandoned when the Alexandria expansion is completed or not. The total cost of the
Westgate upgrading was $1,672,000, of which $861,000 was expended for the oxygen dissolution
and supply systems and reactor tank modifications.
Table 3-3. Operating and Performance Data for Fairfax County, Virginia Oxygen System
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BOD5/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Primary Influent BODs (mg/1)$
TSS
Secondary Effluent BODs (mg/1)
TSS
Design
14
1 74
—
620
—
—
220
173
44
Operation
Aug. 1972 —
July 1973
10.6
2.3
0.54§
469
4480
1 87
161
162
12
19
possible to sample reactor influent as only a baffle separates primary clarifier from reactor
§Based on primary influent BODg rather than reactor influent 6005; indicated value is, therefore,
about 10 percent high.
30
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Gulf States Paper Corporation, Tuscaloosa, Alabama
A custom-designed, self-contained, circular UNOX system was installed at the Gulf States
Paper Corporation complex in Tuscaloosa, Alabama, to treat 9 mgd (0.39 cu m/sec) of unbleached
kraft mill wastewater. This type of wastewater is deficient in nitrogen and phosphorus. To over-
come these deficiencies at Gulf States, phosphoric acid and anhydrous ammonia are added to the
primary effluent.
A custom-designed circular UNOX system differs from one of Union Carbide's modular pack-
age oxygen plants in that it is not a standard off-the-shelf unit. The Gulf States oxygen system is
composed of three above-ground steel tanks each with a diameter of 109 ft (33.2 m), a total depth
of 20 ft (6.1 m), and a SWD of 16 ft (4.9 m). Each tank is divided into a four-stage oxygenation re-
actor and an arcuate clarifier. Three of the four stages are also arcuate; one is circular. Air-lift suc-
tion pickups are used to withdraw settled sludge from the clarifiers. Oxygen dissolution and solids
mixing are accomplished with surface aerators and bottom propellers. A four-bed 30-ton/day
(27.2-metric ton/day) PSA oxygen gas generator and a 43-ton (39-metric ton) liquid oxygen backup
storage tank and atmospheric vaporizer comprise the oxygen supply system.
As shown in the flow diagram presented in Figure 3-5, alum can be dosed to a separate polish-
ing clarifier following secondary clarification for the purpose of effecting additional color removal.
This color removal system has not been used to any great extent to date, however, because of prob-
lems with the alum recovery equipment.
The oxygen system itself has been in operation since October 1974. Following start-up and
"debugging," maintenance requirements have been of a routine nature. Operator attention on the
unit ranges from 7-10 hr/week.
Operating and performance data for the months of April and May 1975 are summarized in
Table 3-4. Although the system is operating at design flow, reactor influent strength has been aver-
aging only about 60 percent of design expectations. It has, therefore, not been necessary to operate
at as high MLSS levels as projected to maintain reasonable F/M loadings. The effluent values shown
represent product quality from the secondary clarifiers. Additional suspended solids removal is
reportedly achieved in passage through the polishing clarifier (operated without alum addition). No
data were available to the writer to document the improvement obtained in the polishing clarifier.
Approximately one-half of the PSA generator output is used in the activated sludge system;
the other half is utilized for black liquor oxidation. Because of the dual role served by the oxygen
supply facilities, the PSA unit was designed to produce 95 percent purity oxygen gas rather than the
standard 90 percent product purity normally associated with PSA operation.
Table 3-4. Operating and Performance Data for Gulf States Paper Oxygen System
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BODs (mg/1)
TSS
Secondary Effluent BODs (mg/1)
TSS
Design
9.0
3.33
0.36
630
4700
1.9
200
100
30
50
Operation
Apr. - May
1975
9.0
3.33
0.37
630
3000
1.2
125
60
12
50
31
-------
PSA GENERATOR 30 TPD
LOXSTORAGE
UNOX REACTORS (3)
NUTRIENT
ADDITION
O2 TO BLACK LIQUOR
OXIDATION
PRIMARYCLARIFIER
CLARIFIERii \
ALUM ADDITION
^
COLOR REMOVAL
THICKENER WASTE ,
SLUDGE
INCINERATOR
FILTER PRESS
ALUM RECOVERY
ASH
Figure 3-5. Flow diagram of the Gulf States Paper Corporation wastewater treatment plant
Tuscaloosa, Alabama.
32
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Lederle Laboratories, Pearl River, New York
Lederle Laboratories, a division of American Cyanamid, manufactures Pharmaceuticals, the
majority of which are antibiotics. The waste stream resulting from production operations has a very
high and variable organic carbon content. The plant wastewater flow which remains relatively con-
stant at about 1.0 mgd (0.044 cu m/sec) can have a BODs loading as high as 32,500 Ib/day (14,
740 kg/day).
Prior to the spring of 1972, an air aeration system was used to treat plant wastes. The daily
operations of this system were marked by persistent odor problems and inconsistent performance,
arising from the highly variable organic load. A UNOX system was designed to replace the existing
air aeration facilities. Start-up occurred in March 1972, which makes it the oldest permanent full-
scale UNOX facility in existence.
A flow diagram of the new oxygenation treatment plant is given in Figure 3-6. The two-train
reactor has overall dimensions of 148 ft long x 74 ft wide x 14.5 ft deep (45 m x 22.6 in x 4.4 m)
with a SWD of 10 ft (3.0 m). The lead reactor stages are larger than the second or third stages to
accommodate the high oxygen demand of the incoming wastewater. Polymers are added ahead of
the single primary clariflocculator to lower the suspended solids concentration entering the second-
ary system as much as possible. The three circular secondary clarifiers each have a 40-ft (12.2-m)
diameter, a 10-ft (3.0-m) SWD, and a plow-type sludge scraper. A 15-ton/day (13.6-metric ton/day)
PSA generator and a 52-ton (47-metric ton) liquid oxygen backup tank provide oxygen supply.
Start-up difficulties included a foaming tendency which ceased once a good biomass had been
established, and mixed liquor solids deposition caused by recycle of large amounts of lime and
alum precipitates in the filtrate from the vacuum filter which are not effectively captured in the
primary clariflocculator. Solids deposition was alleviated by adding bottom mixers to the initially
supplied surface aerators. The PSA oxygen generator experienced upwards of 10 percent outage
following start-up due to valve actuator problems. This unit was one of the first on-line molecu-
lar sieve applications geared to producing oxygen gas for wastewater treatment. As such, some
experimentation was necessary to determine proper lubricating procedures for the valve actua-
tors and to procure sufficienty rugged valve equipment to withstand rapid cycling. Following
final modifications in mid-1973, total unscheduled PSA generator downtime has been reduced
to less than one percent.
Odor complaints from neighboring residents numbered more than 80 in 1971. Complaints have
not been received since the oxygen system went into operation.
A 50 percent sludge recycle rate has been necessary to prevent settled activated sludge from
thickening to concentrations greater than 3-4 percent in the secondary clarifiers. During a three-
month period when the recycle rate was decreased, the clarifier underflow concentration increased
to 5-6 percent. Sludge pumping problems ensued at the higher concentrations, necessitating a return
to the 50 percent rate.
Experienced flow have remained approximately one-third less than design. This has afforded
Lederle the opportunity to remove one reactor train from service during summer months when the
biochemical reaction rate is at its highest level. The partial shutdown action is taken to conserve
energy during the time plant manufacturing energy requirements are greatest. During the remainder
of the year, both trains are kept in service to minimize excess sludge production through operation
at lower F/M loadings. None of the three secondary clarifiers are taken out of operation except for
maintenance.
Average performance data for back-to-back test periods in 1972 are summarized in Table 3-5
for both one-train and two-train operation. Since the 1972 test period, sludge removal problems in
the secondary clarifiers have been corrected. Settled sludge no longer fills up the secondaries and
33
-------
spills over into the polishing clarifier. With the polishing clarifier serving in its intended role, efflu-
ent BOD5 and suspended solids concentrations now generally average around 50 and 10 mg/1,
respectively.
PSA GENERATOR 15 TPD
J
GRIT
INFLUENT CHAMBER
PRIMARY
CLARIFLOCCULATOR
LOX
STORAGE
UNOX REACTOR
EFFLUENT
POLISHING,
RECYCLE SLUDGE
JSECONDARY CLARIFIERS
(3)
L
-FILTRATE
•—^ VACUUM
FILTER
"I
/,
TO LANDFILL
L
WASJE_SI_UDGE_
-«—LIME
"ALUM
SLUDGE CONDITIONING
Figure 3-6. Flow diagram of Lederle Laboratories wastewater treatment plant- Pearl River, New York.
Table 3-5. Operating and Performance Data for Lederle Laboratories Oxygen System
Operation
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BODs (mg/1)
TSS (mg/1)
Polishing Clarifier Effluent BODs (mg/1)
TSS (mg/1)
Design
1.5
13
0.42
540
8000
2.8
1600
—
160
—
2 Trains
Oct. 1972
1.0
19.5
0.17
360
11,500
3.5
1400
800
80
70
1 Train
Nov. 1972
(3 weeks)
1.0
9.75
0.45
360
9600
3.0
1500
1300
90
60
34
-------
Littleton, Colorado
The City of Littleton, Colorado, selected a modular UNOX system for a recent plant expan-
sion. The modular unit used for Littleton is an off-the-shelf package system contained within one
circular above-ground steel tank. The tank, 82 ft (25 m) in diameter x 15 ft (4.6 m) deep [SWD =
12 ft (3.7 m)], is divided by internal walls into a two-stage oxygen reactor, an arcuate secondary
clarifier, a single-stage air aerobic sludge digester, and a chlorine contact chamber. The arcuate
clarifier is equipped with floating bridge mounted air lift suction equipment for withdrawing
settled sludge.
The new oxygen train operates in parallel with two existing trickling filters. Feed to the
trickling filters is first settled in the plant's existing primary clarifier. The oxygen reactor receives
raw degritted municipal wastewater directly. A flow diagram for the Littleton plant is presented in
Figure 3-7.
GRIT CHAMBER
INFLUENT
PRIMARY
"CLARIFIER
TRICKLING FILTERS (2)
FINAL CLARIFIER
SUPERNATANT
I —WASTE SLUDGEfj
AEROBIC
DIGESTER
PRIMARY ANEROBIC DIGESTER
SUPERNATANT
SECONDARY DIGESTER ~
I I
UNOX REACTOR
CHLORINATION
V
/ TO LANDFILL
SLUDGE DRYING BEDS
EFFLUENT
Figure 3-7. Flow diagram of Littleton, Colorado wastewater treatment plant.
35
-------
The combined liquid volume of the two oxygen reactor stages is 97,000 gal (367 cu m). Sur-
face aerators connected by shafts to bottom propellers are employed for oxygen dissolution and
mixing. Due to the small size of the treatment plant, an on-site oxygen gas generating facility was
not provided. Instead, liquid oxygen is trucked in and stored in a 43-ton (39-metric ton) tank, from
where it is directed through an atmospheric vaporizer for conversion to the gaseous form before
entering the oxygenation reactor.
The UNOX package system became operational in Feburary 1974. A major operating diffi-
culty was immediately encountered. The original uncovered air aerobic sludge digester was equipped
with mechanical surface aerators. Aerator icing occurred in the cold Colorado winter climate with
resulting poor volatile suspended solids (VSS) reduction. The problem was rectified by installing a
steel cover over the digester area along with urethane foam insulation and supplementing the sur-
face aerators with an air blower and diffusers to provide adequate air circulation. VSS reductions
have since ranged from 50-60 percent.
Influent flow to the oxygen portion of the Littleton plant has varied from 0.9 mgd (0.04 cu
m/sec) to 1.4 mgd (0.06 cu m/sec) since start-up. The three-month average data summarized in
Table 3-6 for the summer 1975 period indicate the oxygen system is performing within effluent
design specifications.
Table 3-6. Operating and Performance Data for Littleton, Colorado Oxygen System
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BOD§ (mg/1)
TSS
Secondary Effluent BODs (m9/1)
TSS
Design
1.25
1.9
0.6
500
5600
2.8
200
240
20
25
Operation
June-Aug.
1975
1.1
2.16
0.6
440
4000
2.4
160
185
12
24
Morganton, North Carolina
A UNOX facility designed to treat 8 mgd (0.35 cu m/sec) of municipal wastewater combined
with substantial industrial contributions resulting from textiles production and poultry processing
went on-stream at Morganton, North Carolina, in January 1975. As indicated in the plant flow dia-
gram (Figure 3-8), primary clarification was not included in the design. The two-train oxygen reactor
was constructed in an unusual box configuration with four stages per train. Each stage is 44 ft
(13.4 m) square yielding overall length and width dimensions of 88 ft (26.8 m) and 176 ft (53.6 m),
respectively. The total reactor depth is 14 ft (4.3 m) including a 4-ft (1.2-m) freeboard.
Oxygen system equipment consists of surface aerators with bottom impellers for oxygen dis-
solution and mixing and a 26-ton/day (23.6-metric ton/day) PSA generator and 28-ton (25.4-metric
ton) liquid oxygen backup tank for oxygen supply. The PSA generator was outfitted initially with
one one-half size compressor. A second half-size compressor will be added at a later date when plant
flows increase. The two new secondary clarifiers are 80-ft (24.4-m) diameter units with 10-ft
(3.0-m) SWD's and rapid sludge removal and grease skimming capabilities.
36
-------
Process and mechanical reliability have been excellent in the year and half since start-up. PSA
generator availability has exceeded 99.5 percent. A major operational problem in the form of high
fat and grease loadings (often in excess of 100 mg/1) from the local poultry processor, however, has
prevented consistent attainment of effluent quality objectives. No satisfactory method exists for
rejecting these objectionable materials from the secondary system. The fat and grease which are
only slowly bio-degradable pass to the final clarifiers and collect on the liquid surfaces. Although
skimming devices were provided, much of the scum escapes the finals over the weirs taking with it
significant quantities of enmeshed biofloc. Consequently, effluent suspended solids have reached
levels as high as 80-100 mg/1. The problem is further accentuated by a hydraulic regime which
transports final clarifier skimmings to the aerobic digesters and then recycles the digester skimmings
to the plant headworks for recycle through the secondary system.
PSA GENERATOR 26 TPD .
LOX STORAGE
BAR SCREEN
UNOX REACTOR
INFLUENT
RECYCLE SLUDGE
AERATED GRIT
ii 1
CHLORINATION
EFFLUENT
I
AEROBIC
DIGESTERS (2)
SLUDGE
i. I * SECONDARY
-SCUMj | WASTE ^JCLARIFIERS (2)
SCROLL
zf~>\'
POLYMER HCENTRIRJGES(2)' CENTRATE
™F
TO LANDFILL
Figure 3-8. Flow diagram of Morganton, North Carolina wastewater treatment plant.
Efforts to remove a large fraction of the fat and grease load through pretreatment at the poul-
try processing site have been unsuccessful. Consideration is now being given to intercepting the
skimmings from the aerobic digesters and disposing of them separately. When this technique has
been evaluated for short periods on a trial basis, effluent clarity and suspended solids removals
have improved measurably. The difficulties encountered at Morganton appear to the writer to con-
stitute a compelling argument for the inclusion of primary clarification facilities in any future
designs faced with similar wastewater characteristics.
37
-------
Two months of operating and performance data are summarized in Table 3-7. Effluent quality
documented for March 1975 is typical of months when the influent grease load has been somewhat
lower than normal and represents about the best performance level that can be achieved under
present conditions. In April 1975, the influent grease load was up, and the monthly average effluent
suspended solids concentration increased accordingly. The much higher than anticipated influent
suspended solids concentrations for these two months indicate that primary clarification would
probably have been a desirable and justifiable feature aside from grease removal considerations.
Table 3-7. Operating and Performance Data for Morganton, North Carolina Oxygen System
Operation
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reacotr Influent BODs (mg/1)
TSS (mg/1)
Secondary Effluent BODs (m9/1)
TSS (mg/1)
Design
8.0
3.5
0.53
800
6000
3.0
350
400
27
25
March
1975
4.7
6.0
0.31
470
5600
2.1
364
836
42
29
April
1975
5.9
4.7
0.33
590
6400
1.6
357
946
32
79
North Lauderdale, Florida
An off-the-shelf modular UNOX system was installed at North Lauderdale, Florida, to serve a
population base of approximately 10,000 people. This package system consists of a two-stage
oxygen reactor, an arcuate secondary clarifier, and an uncovered single-stage air aerobic sludge
digester. The arcuate clarifier has an air lift suction device mounted from a floating bridge for re-
moving settled sludge. The air aerobic digester is equipped only with mechanical surface aerators: it
was not necessary to provide supplemental compressed air as at Littleton.
The entire secondary complex is contained within one circular, 95-ft (29-m) diameter, 15-ft
(4.6-m) deep, above-ground steel tank. The tank's SWD is 12 ft (3.7 m). Unlike the Littleton modu-
lar unit, a separate external chlorine contact chamber was provided rather than including it in the
package system. Granular media filters are available for effluent polishing, although to date they
have not been used. Raw degritted municipal waste water is fed directly to the oxygen system. Ex-
cess activated sludge is dewatered either by centrifugation or on sand drying beds. A flow diagram
of the new North Lauderdale treatment plant is shown in Figure 3-9.
Oxygen dissolution and mixing are accomplished in the 129,000-gal (488-cu m) oxygen re-
actor with surface aerators and supplemental bottom agitators. A 43-ton (39-metric ton) liquid
oxygen storage tank and attendant atmospheric vaporizer comprise the oxygen supply system.
The plant was placed in operation in early July 1975. To date, influent flow has been averaging
only about 65 percent of the design flow of 2 mgd (0.09 cu m/sec), although wastewater strength
has been somewhat higher than anticipated. No significant operating problems have been encount-
ered. Performance as exhibited by the average data for September 1975 shown in Table 3-8 has
been excellent.
38
-------
BAR SCREEN
INFLUENT-^
COMMINUTOR
UNOXREACTOR
fO\
\- SLUDGE
CENTRIFUGES/ r
TO LANDFILL
AEROBIC
DIGESTER
DRYING BEDS
I i_
CHLORINE INJECTION
CHLORINE CONTACT CHAMBER
Figure 3-9. Flow diagram of North Lauderdale, Florida wastewater treatment plant.
Table 3-8. Operating and Performance Data for North Lauderdale, Florida Oxygen System
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BOD5 (mg/1)
TSS (mg/1)
Secondary Effluent BOD5 (mg/1)
TSS (mg/1)
Design
2.0
1.56
0.68
525
5600
2
200
130
20
20
Operation
Sept. 1975
1.3
2.4
0.68
541
4500
1.5*
245
180
<10
-dO
return sludge rate
39
-------
Speedway, Indiana
In June 1972, a new 7.5 mgd (0.33 cu ni/sec) UNOX installation was placed in operation at
Speedway, Indiana. This was the first municipal UNOX facility to be completed. Of all the oxygen-
activated sludge wastewater treatment systems now in operation, the Speedway plant was preceded
only by the municipal OASES plant at Fairfax County, Virginia, and the industrial UNOX plant at
the Lederle Laboratories in Pearl River, New York.
The flow diagram in Figure 3-10 indicates that the Speedway oxygen system is of conventional
design. The two-train oxygen reactor is preceded by primary clarification. Three of the six primaries
are existing units; the other three are converted secondary clarifiers from the City's old trickling
filter treatment facility. Each of the four reactor stages per train is 22 ft (6.7 m) square with a 16-ft
(4.9-m) SWD. The overall dimensions of the two reactor tanks taken together are 88 ft long x 44 ft
wide x 20 ft deep (26.8 m x 13.4 m x 6.1 m). Three new 65-ft (19.8-m) diameter, 10-ft (3.0-m)
SWD secondary clarifiers with the increasingly popular rapid method of removing settled sludge
were provided. At a future data as needed, plant capacity can be increased to 10 mgd (0.44 cu m/
sec) by the construction of one additional secondary clarifier.
PSA GENERATOR 5 TPD
LOXSTORAGE
PRIMARY CLARIFIERS (6)
GRIT
REMOVAL
INFLUENT!
SCREEN
UNOXREACTOR
MIXED !
SLUDGE
I
SECONDARY CLARIFIERS
WASTE SLUDGE)
I T
[EFFLUENT
I
J
..CHLORINATION-
\ >-
(3)
RECYCLE SLUDGE
HOLDING SUPERNATANT/~>v
TANKS (2) ZIMPRO ^
i
V
(HOLDING //VACUUM
FILTRATE ll_IANK_/ ' FILTER
Figure 3-10. Flow diagram of Speedway, Indiana wastewater treatment plant.
40
-------
The UNOX reactors were designed to use surface aerators attached by shafts to bottom agita-
tors for oxygen dissolution and mixing. A three-bed 5-ton/day (4.4-metric ton/day) PSA unit gen-
erates oxygen gas on-site. A 7-ton (6.4-metric ton) liquid oxygen storage tank and accompanying
atmospheric vaporizer were furnished for reserve. Profiting from difficulties experienced with
earlier four-bed PSA generator designs at Lederle Laboratories and on a U.S. EPA co-sponsored
demonstration grant project at the Newtown Creek plant in Brooklyn, New York (3), particularly
as related to valves and lubricants, the second generation three-bed design employed at Speedway
has proven to be highly reliable with less than 1-1/2 percent total downtime for scheduled and un-
scheduled maintenance.
Waste activated sludge is recycled to the primaries for co-thickening with raw sludge. The
mixed kludges are then pumped to a holding tank which feed a Zimpro wet oxidation system design-
ed to condition sludge for dewatering. Conditioned sludge is dewatered by vacuum filtration prior
to being trucked to landfill. Periodic and lengthy shutdowns of the wet oxidation system placed
considerable stress on the main stream treatment components for much of the early history of this
new facility. Unable to truck liquid sludges away, it was frequently necessary to return mixed raw
and waste sludges from the sludge holding tank to the primary clarifiers. When the primaries filled
up, sludge overflowed into the oxygen reactors along with primary effluent. The oxygenation tanks
during these periods in effect served more as aerobic sludge digesters than conventional activated
sludge systems.
Considering the difficulties imposed by the above conditions on the management of second-
ary sludge inventory, oxygen system performance was superb. Annual average effluent BOD5 and
suspended solids concentrations were low in both 1973 and 1974, as indicated in Table 3-9. The
highest monthly average BOD5 and suspended solids levels recorded in these two years were 16 and
30 mg/1, respectively. Also shown in Table 3-9 are the results of one month of one-train operation
in early 1976. Occasional one-train operating tests have been conducted by plant personnel to
evaluate oxygen system performance at loadings comparable to design values.
Table 3-9. Operating and Performance Data for Speedway, Indiana Oxygen System
Operation
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BOD5/day/ke MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (mg/1)
Reactor Influent BOD5 (mg/1
TSS (mg/1)
Secondary Effluent BOD5 (mg/1)
TSS (mg/1)
Design
7.5
1.48
0.51
750
4200
2.2
110
96
15
20
2
1973
4.4
2.52
0.20
440
6080
1.54
91
179
9
16
Trains*
1974
4.6
2.41
0.51
460
6600
1.3
73
109
9
14
1 Traint
Jan. 16 -
Feb. 18, 1976
4.3
1.29
0;70
645
4760
1.66"
114
118
13
18
'Three secondary clarifiers in operation
|Two secondary clarifiers in operation
« Excludes reported values for Feb. 6, 7, 8 and 9
41
-------
Union Carbide Corporation, Sistersville, West Virginia
The Chemicals and Plastics Division of the Union Carbide Corporation placed a UNOX system
in operation in November 1973 to treat waste products from the'manufacture of silicones. The re-
sulting wastewater stream has a high organic carbon content and also contains substantial quantities
of acid and various oils. Conditioning is necessary ahead of the biological process to neutralize the
acid and remove the oil. A holding pond (not included in the flow diagram shown in Figure 3-11) is
utilized for diversion of large spills that cannot be adequately preconditioned.
This inhouse Carbide project marked the first utilization of circular reactor/clarifier UNOX
combination tanks. Two such units were installed, each consisting of three arcuate reactor stages
and one circular reactor stage and an arcuate final clarifier. In contrast to the above-ground designs
employed in later circular UNOX facilities (refer to Gulf Stages Paper Corporation; Littleton,
Colorado; and North Lauderdale, Florida), the Sistersville tanks were installed in conventional
below-ground fashion. The custom-designed dimensions of the Sistersville units are: diameter —
102 ft (31.1 m), total depth - 14 ft (4.3 m), and SWD - 10 ft (3.1 m). The final clarifiers are
equipped with airlift suction equipment for removing settled sludge.
CRYOGENIC GENERATOR 15 TPD
(N2 + 02)
N2
LOX STORAGE
LIME ADDITION
PRIMARY API
SEPARATOR
NUTRIENT
ADDITION
EQUILIZATION I
BASIN i
UNOX REACTORS (2)
HOLDING BASIN
INFLUENT
SUPERNATANT
DEWATERING
ITO LANDFILL
Figure 3-11. Flow diagram of Union Carbide Corporation wastewater treatment plant
Sistersville, West Virginia.
42
-------
Surface aerators connected to bottom impellers are used to achieve oxygen dissolution and
oxygen and biomass dispersion. Oxygen is supplied in a rather unusual manner from an on-site
industrial cryogenic nitrogen gas generator which produces 15 tons/day (13.6 metric tons/day) of
oxygen gas as a by-product. Prior to start-up of the silicones wastewater treatment facility, the by-
product oxygen was wasted to the atmosphere.
Problems were initially encountered with the floating bridge mechanism from which the sludge
scraping and pickup devices are supported. Corrective action required redesign and relocation of the
bridge center support. Later arcuate clarifier designs profited from the Sistersville experiences.
Occasional toxic spills, primarily from copper, have resulted in biological upsets. The oxygen-
activated sludge system has usually recovered from these spills within one week. Following an in-
plant survey, a program is underway to eliminate copper from plant discharges in concentrations
which are toxic to microorganisms.
Average monthly operating and performance data for August and December 1975 are pre-
sented in Table 3-10. At influent loadings equal to 85-95 percent of hydraulic capacity, effluent
quality has been significantly better than required by the design specifications. The difficulty in
settling silicone fines can be noted in the effluent suspended solids levels which are two to three
times the effluent BOD 5 concentrations.
Table 3-10. Operating and Performance Data for Union Carbide Sistersville Oxygen System
Operation
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BODs (mg/1)
TSS (mg/1)
Secondary Effluent BOD5 (mg/1)
TSS (mg/1)
Design
4.3
3.5
0.85
600
5000
2.0
370
<100
50
<100
Aug. 1975
3.6
4.2
0.75
502
4500
1.0*
425
75
25
70
Dec. 1975
4.1
3.7
0.90
572
3900
2.0
339
103
20
43
JHigh sludge return rate
Winnipeg, Manitoba
One of the more attractive oxygen-activated sludge plants now in operation is located at Winni-
peg, Manitoba, Canada. This 12-mgd (0.53-cu m/sec) treatment facility was designed to operate over
a wide air temperature range (100° F in summer to -50° F in winter) and is, therefore, totally
housed with the exception of the covered UNOX reactor.
The plant utilizes a conventional flow scheme to treat municipal wastewater. Primary clarifi-
cation is utilized ahead of a two-train, three-stage/train, oxygenation reactor having overall dimen-
sions of 120 ft long x 60 ft wide x 19.5 ft deep (36.6 m x 18.3 m x 5.9 m). The reactor's SWD is
16 ft (4.9 m). Mixed liquor flow is evenly divided between two 110-ft (33.5-m) diameter final
clarifiers. The SWD of the finals is 10 ft (3.0 m). As with most recently-constructed circular clari-
fiers, rapid sludge removal equipment was provided rather than the older plow-type scrapers. Pri-
mary and waste activated sludges are mixed and centrifuged before undergoing incineration. The
flow diagram for the plant is given in Figure 3-12.
43
-------
The UNOX system components selected for Winnipeg includes surface aerators and bottom
mixers for oxygen dissolution and a 10-ton/day (9.1 -metric ton/day) PSA oxygen gas generator and
14-ton (12.7-metric ton) liquid oxygen backup tank for oxygen supply. Considerable difficulty has
been experienced with the operation of the PSA compressor. This machine was initially outfitted
with internal clearance pocket unloaders. These unloaders did not function properly resulting in the
imposition of undue stress on and excessive wear of compressor bearings and bushings. Frequent
outages were necessary to overhaul the worn parts. Eventually in late 1975, the compressor was
completely rebuilt and the clearance pocket unloaders replaced with suction pocket unloaders.
Except for one subsequent unscheduled outage due to a heater failure, the compressor has worked
well since then.
System start-up occurred in September 1974. No process related difficulties have been en-
countered. Operation at cold mixed liquor temperatures down to 10° C has not induced growth of
filamentous organisms or any other noticeable sludge settling problems. In each 1975, official one-
month performance tests were conducted with only one reactor train in service and with both
reactor trains in service. Both final clarifiers were used during each test. The results of the tests are
documented in Table 3-11. In each case, although the aeration detention time was less than the F/M
loading higher than design, effluent BOD5 and suspended solids concentrations were significantly
lower than required by design stipulations.
PSA GENERATOR 12 TPD
LOX STORAGE
PRE-CHLORINATION
AERATED
GRIT PRIMARY
CHAMBER CLARIFIERS
INFLUENT
BAR IGRIT PRIMARY!
SCREENS 11 SLUDGE
IT
t-*-
1
r~
1 /
1 s
r~
!,
UNOX REACTOR
„ 1
1
2
-»•-
2 _
\
»
3
.^3
., .
n
L.
FINAL CLARIFIERS (2)
SLUDGE HOLDING TANK | WASTE
I --- 1 - I SLUDGE
r -1
I ) MIXED
X/ SLUDGE
-RECYCLE J3LAJDGEJ
CHLORINATION
EFFLUENT!
CENTR1FUGE
TO MAIN PLANT INCINERATOR
Figure 3-12. Flow diagram of Winnipeg, Manitoba wastewater treatment plant.
44
-------
Table 3-11. Operating and Performance Data for Winnipeg, Manitoba Oxygen System
Operation
Parameter
Influent Flow (mgd)
Aeration Detention Time, Q (hr)
F/M Loading (kg BODs/day/kg MLVSS)
Secondary Clarifier Overflow Rate (gpd/sq ft)
MLSS (mg/1)
Return Sludge TSS (%)
Reactor Influent BOD5 (mg/1)
TSS (mg/1)
Secondary Effluent BODs (mg/1)
TSS (mg/1)
Design
12
1.74
0.46
630
5000
2.2
133
100
25
30
1 Reactor
Train:}:
Jan. 1975
8.5
1.23
0.99
446
5950
1.9
244
290
20
17
2 Reactor
Trains:}:
Apr. 1975
13.4
1.59
0.62
704
5100
1.6
150
193
17
13
^Both final clarifiers in service
INFORMATION SOURCES
Information on oxygen systems in various stages of implementation was supplied by the Union
Carbide Corporation; Air Products and Chemicals, Inc.; and the FMC Corporation. Case history data
and flow diagrams for UNOX plants in operation were provided by the Union Carbide Corporation.
Case history data and pertinent diagrams for the OASES plant at Fairfax County, Virginia, were
extracted from the final report for U.S. EPA Contract No. 68-03-0405. Process design and equip-
ment criteria for and visual representations of the MAROX process were taken from FMC Corpora-
tion advertising literature (4), supplemented by information derived from personal communications
with FMC. Progress reports and other information on file at the U.S. EPA's Municipal Environmen-
tal Research Laboratory for Grant No. S803910 formed the basis of the discussion of Metropolitan
Denver's MAROX demonstration project. Flow and dimensioned diagrams of the Denver MAROX
test bay were reprinted from an FMC project bulletin (6).
The assistance of staff members of the above three firms who contributed in supplying the
above described information is gratefully acknowledged. The cooperation of Richard Kaptain,
Assistant Plant Manager for the City of Decatur, Illinois, in providing additional details for the
Decatur UNOX case history is also appreciated.
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REFERENCES
1. Albertsson, J.G., McWhirter, J.R., Robinson, E.K., and Vahldieck, N.P., "Investigation of the
Use of High Purity Oxygen Aeration in the Conventional Activated Sludge Process," Water
Pollution Control Research Series Report No. 17050 DNW 05/70, Federal Water Quality
Administration, Cincinnati, Ohio, May 1970.
2. Brenner, R.C., "Summary Description of Oxygen Aeration Systems in the United States,"
Proceedings of the Second U.S.-Japan Conference on Sewage Treatment Technology, Cincin-
nati, Ohio, December 1972.
3. Brenner, R.C., "EPA Experiences in Oxygen-Activated Sludge," Prepared for Office of Tech-
nology Transfer Design Seminar Program, U.S. Environmental Protection Agency, Cincinnati,
Ohio, October 1974.
4. FMC Corporation, "FMC Pure Oxygen Wastewater Treatment in Open Tanks," FMC Bulletin
8000-A, Itasca, Illinois, 1976.
5. FMC Corporation, "FMC Pure Oxygen System at Metropolitan Denver Sewage Disposal Dis-
trict No. 1," FMC Project Report 8000.1, Itasca, Illinois, 1976.
6. McDowell, C.S., and Giannelli, J., "Oxygen-Activated Sludge Plant Completes Two Years of
Successful Operation," Draft Report for Contract No. 68-03-0405 with Air Products and
Chemicals, Inc., U.S. Environmental Protection Agency, Cincinnati, Ohio, Publication Pending.
•&U.S. GOVERNMENT PRINTING OFFICE: 1977-757-056/6565 Region No. 5-1 I
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